copy from dom/base/UseCounters.conf
copy to dom/base/UseCountersWorker.conf
--- a/dom/base/UseCounters.conf
+++ b/dom/base/UseCountersWorker.conf
@@ -13,81 +13,38 @@
 //   (b) a comment, which is a line that begins with "//"
 //
 //   (c) one of four possible use counter declarations:
 //
 //         method <IDL interface name>.<IDL operation name>
 //         attribute <IDL interface name>.<IDL attribute name>
 //         custom <any valid identifier> <description>
 //
-// The <description> for custom counters will be appended to "Whether a document "
-// or "Whether a page ", so phrase it appropriately.  For instance, "constructs a
-// Foo object" or "calls Document.bar('some value')".  It may contain any
-// character (including whitespace).
+// The <description> for custom counters will be appended to "Whether a
+// dedicated worker " or "Whether a shared worker" or "Whether a service worker
+//  ", so phrase it appropriately.  For instance, "constructs a
+// Foo object" or "calls Bar.baz('some value')". It may contain any character
+// (including whitespace).
 //
 // To actually cause use counters to be incremented, DOM methods
-// and attributes must have a [UseCounter] extended attribute in
-// the Web IDL file.
+// and attributes must have a [UseCounter] extended attribute and be exposed to
+// workers in the Web IDL file.
 // Custom counters are incremented when
-// SetUseCounter(eUseCounter_custom_MyName) is called on a Document object.
+// SetUseCounter(UseCounterWoker::Custom_MyName) is called on a WorkerPrivate
+// object.
 //
 // You might reasonably ask why we have this file and we require
 // annotating things with [UseCounter] in the relevant WebIDL file as
 // well.  Generating things from bindings codegen and ensuring all the
 // dependencies were correct would have been rather difficult.
 
-method SVGSVGElement.getElementById
-attribute SVGSVGElement.currentScale
-
 // Push API
 method PushManager.subscribe
 method PushSubscription.unsubscribe
 
-// window.sidebar
-attribute Window.sidebar
-
-// AppCache API
-method OfflineResourceList.swapCache
-method OfflineResourceList.update
-attribute OfflineResourceList.status
-attribute OfflineResourceList.onchecking
-attribute OfflineResourceList.onerror
-attribute OfflineResourceList.onnoupdate
-attribute OfflineResourceList.ondownloading
-attribute OfflineResourceList.onprogress
-attribute OfflineResourceList.onupdateready
-attribute OfflineResourceList.oncached
-attribute OfflineResourceList.onobsolete
-
-// Non-standard IndexedDB API
-method IDBDatabase.createMutableFile
-method IDBDatabase.mozCreateFileHandle
-method IDBMutableFile.open
-method IDBMutableFile.getFile
-
-// DataTransfer API (gecko-only methods)
-method DataTransfer.addElement
-attribute DataTransfer.mozItemCount
-attribute DataTransfer.mozCursor
-method DataTransfer.mozTypesAt
-method DataTransfer.mozClearDataAt
-method DataTransfer.mozSetDataAt
-method DataTransfer.mozGetDataAt
-attribute DataTransfer.mozUserCancelled
-attribute DataTransfer.mozSourceNode
-
-// Marquee events
-custom onstart sets a <marquee> onstart event listener
-custom onbounce sets a <marquee> onbounce event listener
-custom onfinish sets a <marquee> onfinish event listener
-
-// JavaScript feature usage
-custom JS_asmjs uses asm.js
-custom JS_wasm uses WebAssembly
-
 // Console API
 method console.assert
 method console.clear
 method console.count
 method console.countReset
 method console.debug
 method console.error
 method console.info
@@ -103,242 +60,8 @@ method console.groupEnd
 method console.time
 method console.timeLog
 method console.timeEnd
 method console.exception
 method console.timeStamp
 method console.profile
 method console.profileEnd
 
-// document.open information
-custom DocumentOpen calls document.open in a way that creates a new Window object
-
-// HTMLDocument named getter
-custom HTMLDocumentNamedGetterHit calls to the named getter on HTMLDocument that find something via the name lookup
-
-custom FilteredCrossOriginIFrame cross-origin <iframe> within a CSS/SVG filter
-
-// Custom Elements
-method CustomElementRegistry.define
-
-// Shadow DOM
-method Element.attachShadow
-
-// Media Device Access
-method MediaDevices.enumerateDevices
-custom EnumerateDevicesInsec calls MediaDevices.enumerateDevices from an insecure context
-custom EnumerateDevicesUnfocused calls MediaDevices.enumerateDevices from a unfocused document
-method MediaDevices.getUserMedia
-method Navigator.mozGetUserMedia
-custom GetUserMediaUnfocused calls MediaDevices.getUserMedia from an unfocused document
-custom GetUserMediaInsec calls MediaDevices.getUserMedia from an insecure context
-custom MozGetUserMediaInsec calls Navigator.mozGetUserMedia from an insecure context
-custom GetUserMediaXOrigin calls MediaDevices.getUserMedia from a cross origin context
-custom MozGetUserMediaXOrigin calls Navigator.mozGetUserMedia from a cross origin context
-method MediaDevices.getDisplayMedia
-custom GetDisplayMediaXOrigin calls MediaDevices.getDisplayMedia from a cross origin context
-
-// Missing-property use counters.  We claim these are "method" use
-// counters, because we don't need a separate description string for
-// them and we only need one use counter, not a getter/setter pair.
-method HTMLDocument.adoptedStyleSheets
-method HTMLDocument.caretRangeFromPoint
-method HTMLDocument.clear
-method HTMLDocument.exitPictureInPicture
-method HTMLDocument.featurePolicy
-method HTMLDocument.onbeforecopy
-method HTMLDocument.onbeforecut
-method HTMLDocument.onbeforepaste
-method HTMLDocument.oncancel
-method HTMLDocument.onfreeze
-method HTMLDocument.onmousewheel
-method HTMLDocument.onresume
-method HTMLDocument.onsearch
-method HTMLDocument.onsecuritypolicyviolation
-method HTMLDocument.onwebkitfullscreenchange
-method HTMLDocument.onwebkitfullscreenerror
-method HTMLDocument.pictureInPictureElement
-method HTMLDocument.pictureInPictureEnabled
-method HTMLDocument.registerElement
-method HTMLDocument.wasDiscarded
-method HTMLDocument.webkitCancelFullScreen
-method HTMLDocument.webkitCurrentFullScreenElement
-method HTMLDocument.webkitExitFullscreen
-method HTMLDocument.webkitFullscreenElement
-method HTMLDocument.webkitFullscreenEnabled
-method HTMLDocument.webkitHidden
-method HTMLDocument.webkitIsFullScreen
-method HTMLDocument.webkitVisibilityState
-method HTMLDocument.xmlEncoding
-method HTMLDocument.xmlStandalone
-method HTMLDocument.xmlVersion
-method Window.AbsoluteOrientationSensor
-method Window.Accelerometer
-method Window.ApplicationCache
-method Window.ApplicationCacheErrorEvent
-method Window.Atomics
-method Window.AudioParamMap
-method Window.AudioWorklet
-method Window.AudioWorkletNode
-method Window.BackgroundFetchManager
-method Window.BackgroundFetchRecord
-method Window.BackgroundFetchRegistration
-method Window.BeforeInstallPromptEvent
-method Window.Bluetooth
-method Window.BluetoothCharacteristicProperties
-method Window.BluetoothDevice
-method Window.BluetoothRemoteGATTCharacteristic
-method Window.BluetoothRemoteGATTDescriptor
-method Window.BluetoothRemoteGATTServer
-method Window.BluetoothRemoteGATTService
-method Window.BluetoothUUID
-method Window.CanvasCaptureMediaStreamTrack
-method Window.chrome
-method Window.clientInformation
-method Window.ClipboardItem
-method Window.CSSImageValue
-method Window.CSSKeywordValue
-method Window.CSSMathInvert
-method Window.CSSMathMax
-method Window.CSSMathMin
-method Window.CSSMathNegate
-method Window.CSSMathProduct
-method Window.CSSMathSum
-method Window.CSSMathValue
-method Window.CSSMatrixComponent
-method Window.CSSNumericArray
-method Window.CSSNumericValue
-method Window.CSSPerspective
-method Window.CSSPositionValue
-method Window.CSSRotate
-method Window.CSSScale
-method Window.CSSSkew
-method Window.CSSSkewX
-method Window.CSSSkewY
-method Window.CSSStyleValue
-method Window.CSSTransformComponent
-method Window.CSSTransformValue
-method Window.CSSTranslate
-method Window.CSSUnitValue
-method Window.CSSUnparsedValue
-method Window.CSSVariableReferenceValue
-method Window.defaultStatus
-// See comments in Window.webidl about why this is disabled.
-//method Window.defaultstatus
-method Window.DeviceMotionEventAcceleration
-method Window.DeviceMotionEventRotationRate
-method Window.DOMError
-method Window.EnterPictureInPictureEvent
-method Window.External
-method Window.FederatedCredential
-method Window.Gyroscope
-method Window.HTMLContentElement
-method Window.HTMLDialogElement
-method Window.HTMLShadowElement
-method Window.ImageCapture
-method Window.InputDeviceCapabilities
-method Window.InputDeviceInfo
-method Window.Keyboard
-method Window.KeyboardLayoutMap
-method Window.LinearAccelerationSensor
-method Window.Lock
-method Window.LockManager
-method Window.MediaMetadata
-method Window.MediaSession
-method Window.MediaSettingsRange
-method Window.MIDIAccess
-method Window.MIDIConnectionEvent
-method Window.MIDIInput
-method Window.MIDIInputMap
-method Window.MIDIMessageEvent
-method Window.MIDIOutput
-method Window.MIDIOutputMap
-method Window.MIDIPort
-method Window.NavigationPreloadManager
-method Window.NetworkInformation
-method Window.offscreenBuffering
-method Window.OffscreenCanvas
-method Window.OffscreenCanvasRenderingContext2D
-method Window.onappinstalled
-method Window.onbeforeinstallprompt
-method Window.oncancel
-method Window.ondeviceorientationabsolute
-method Window.onmousewheel
-method Window.onsearch
-method Window.onselectionchange
-method Window.openDatabase
-method Window.OrientationSensor
-method Window.OverconstrainedError
-method Window.PasswordCredential
-method Window.PaymentAddress
-method Window.PaymentInstruments
-method Window.PaymentManager
-method Window.PaymentMethodChangeEvent
-method Window.PaymentRequest
-method Window.PaymentRequestUpdateEvent
-method Window.PaymentResponse
-method Window.PerformanceEventTiming
-method Window.PerformanceLongTaskTiming
-method Window.PerformancePaintTiming
-method Window.PhotoCapabilities
-method Window.PictureInPictureWindow
-method Window.Presentation
-method Window.PresentationAvailability
-method Window.PresentationConnection
-method Window.PresentationConnectionAvailableEvent
-method Window.PresentationConnectionCloseEvent
-method Window.PresentationConnectionList
-method Window.PresentationReceiver
-method Window.PresentationRequest
-method Window.RelativeOrientationSensor
-method Window.RemotePlayback
-method Window.ReportingObserver
-method Window.RTCDtlsTransport
-method Window.RTCError
-method Window.RTCErrorEvent
-method Window.RTCIceTransport
-method Window.RTCSctpTransport
-method Window.Sensor
-method Window.SensorErrorEvent
-method Window.SharedArrayBuffer
-method Window.styleMedia
-method Window.StylePropertyMap
-method Window.StylePropertyMapReadOnly
-method Window.SVGDiscardElement
-method Window.SyncManager
-method Window.TaskAttributionTiming
-method Window.TextDecoderStream
-method Window.TextEncoderStream
-method Window.TextEvent
-method Window.Touch
-method Window.TouchEvent
-method Window.TouchList
-method Window.TransformStream
-method Window.USB
-method Window.USBAlternateInterface
-method Window.USBConfiguration
-method Window.USBConnectionEvent
-method Window.USBDevice
-method Window.USBEndpoint
-method Window.USBInterface
-method Window.USBInTransferResult
-method Window.USBIsochronousInTransferPacket
-method Window.USBIsochronousInTransferResult
-method Window.USBIsochronousOutTransferPacket
-method Window.USBIsochronousOutTransferResult
-method Window.USBOutTransferResult
-method Window.UserActivation
-method Window.visualViewport
-method Window.webkitCancelAnimationFrame
-method Window.webkitMediaStream
-method Window.WebKitMutationObserver
-method Window.webkitRequestAnimationFrame
-method Window.webkitRequestFileSystem
-method Window.webkitResolveLocalFileSystemURL
-method Window.webkitRTCPeerConnection
-method Window.webkitSpeechGrammar
-method Window.webkitSpeechGrammarList
-method Window.webkitSpeechRecognition
-method Window.webkitSpeechRecognitionError
-method Window.webkitSpeechRecognitionEvent
-method Window.webkitStorageInfo
-method Window.Worklet
-method Window.WritableStream

--- a/dom/base/usecounters.py
+++ b/dom/base/usecounters.py
@@ -38,29 +38,35 @@ def read_conf(conf_filename):
                 yield { 'type': 'custom',
                         'name': name,
                         'desc': desc }
                 continue
             raise ValueError('error parsing %s at line %d' % (conf_filename, line_num))
 
     return parse_counters(stream)
 
-def generate_histograms(filename):
+def generate_histograms(filename, is_for_worker=False):
     # The mapping for use counters to telemetry histograms depends on the
     # ordering of items in the dictionary.
+
+    # The ordering of the ending for workers depends on the WorkerType defined
+    # in WorkerPrivate.h.
+    endings = ["DEDICATED_WORKER", "SHARED_WORKER", "SERVICE_WORKER"] if is_for_worker else ["DOCUMENT", "PAGE"]
+
     items = collections.OrderedDict()
     for counter in read_conf(filename):
         def append_counter(name, desc):
             items[name] = { 'expires_in_version': 'never',
                             'kind' : 'boolean',
                             'description': desc }
 
         def append_counters(name, desc):
-            append_counter('USE_COUNTER2_%s_DOCUMENT' % name, 'Whether a document %s' % desc)
-            append_counter('USE_COUNTER2_%s_PAGE' % name, 'Whether a page %s' % desc)
+            for ending in endings:
+                append_counter('USE_COUNTER2_%s_%s' % (name, ending),
+                               'Whether a %s %s' % (ending.replace('_', ' ').lower(), desc))
 
         if counter['type'] == 'method':
             method = '%s.%s' % (counter['interface_name'], counter['method_name'])
             append_counters(method.replace('.', '_').upper(), 'called %s' % method)
         elif counter['type'] == 'attribute':
             attr = '%s.%s' % (counter['interface_name'], counter['attribute_name'])
             counter_name = attr.replace('.', '_').upper()
             append_counters('%s_getter' % counter_name, 'got %s' % attr)

--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -11982,16 +11982,26 @@
     "high": 2000,
     "n_buckets": 25,
     "keyed": true,
     "releaseChannelCollection": "opt-out",
     "alert_emails": ["sw-telemetry@mozilla.com"],
     "description": "Time (in ms) measured between when the fetch handler finished executing and when we reset the network channel."
   },
 
+  "SERVICE_WORKER_DESTROYED": {
+    "record_in_processes": ["main", "content"],
+    "products": ["firefox", "fennec", "geckoview"],
+    "expires_in_version": "never",
+    "kind": "count",
+    "releaseChannelCollection": "opt-out",
+    "bug_numbers": [1202706],
+    "alert_emails": ["tdsmith@mozilla.com", "compatibility@lists.mozilla.org"],
+    "description": "Number of service workers destroyed; used in conjunction with use counter histograms"
+  },
   "ONBEFOREUNLOAD_PROMPT_ACTION" : {
     "record_in_processes": ["main", "content"],
     "products": ["firefox", "fennec", "geckoview"],
     "expires_in_version": "45",
     "kind": "enumerated",
     "n_values": 3,
     "description": "What button a user clicked in an onbeforeunload prompt.  (Stay on Page = 0, Leave Page = 1, prompt aborted = 2)"
   },
@@ -12537,25 +12547,45 @@
     "record_in_processes": ["main", "content"],
     "products": ["firefox", "fennec", "geckoview"],
     "alert_emails": ["amarchesini@mozilla.com"],
     "bug_numbers": [1286895],
     "expires_in_version": "never",
     "kind": "count",
     "description": "Tracking whether a SharedWorker spawn gets queued due to hitting max workers per domain limit. File bugs in Core::DOM in case of a Telemetry regression."
   },
+  "SHARED_WORKER_DESTROYED": {
+    "record_in_processes": ["main", "content"],
+    "products": ["firefox", "fennec", "geckoview"],
+    "expires_in_version": "never",
+    "kind": "count",
+    "releaseChannelCollection": "opt-out",
+    "bug_numbers": [1202706],
+    "alert_emails": ["tdsmith@mozilla.com", "compatibility@lists.mozilla.org"],
+    "description": "Number of shared workers destroyed; used in conjunction with use counter histograms"
+  },
   "DEDICATED_WORKER_SPAWN_GETS_QUEUED": {
     "record_in_processes": ["main", "content"],
     "products": ["firefox", "fennec", "geckoview"],
     "alert_emails": ["amarchesini@mozilla.com"],
     "bug_numbers": [1286895],
     "expires_in_version": "never",
     "kind": "count",
     "description": "Tracking whether a DedicatedWorker spawn gets queued due to hitting max workers per domain limit. File bugs in Core::DOM in case of a Telemetry regression."
   },
+  "DEDICATED_WORKER_DESTROYED": {
+    "record_in_processes": ["main", "content"],
+    "products": ["firefox", "fennec", "geckoview"],
+    "expires_in_version": "never",
+    "kind": "count",
+    "releaseChannelCollection": "opt-out",
+    "bug_numbers": [1202706],
+    "alert_emails": ["tdsmith@mozilla.com", "compatibility@lists.mozilla.org"],
+    "description": "Number of dedicated workers destroyed; used in conjunction with use counter histograms"
+  },
   "SERVICE_WORKER_REGISTRATIONS": {
     "record_in_processes": ["main", "content"],
     "products": ["firefox", "fennec", "geckoview"],
     "expires_in_version": "50",
     "kind": "count",
     "description": "Count how many registrations occurs. File bugs in Core::DOM in case of a Telemetry regression."
   },
   "SERVICE_WORKER_CONTROLLED_DOCUMENTS": {

--- a/toolkit/components/telemetry/build_scripts/gen_histogram_enum.py
+++ b/toolkit/components/telemetry/build_scripts/gen_histogram_enum.py
@@ -35,64 +35,75 @@ namespace Telemetry {
 """
 
 footer = """
 } // namespace mozilla
 } // namespace Telemetry
 #endif // mozilla_TelemetryHistogramEnums_h"""
 
 
+def get_histogram_typename(histogram):
+    name = histogram.name()
+    if name.startswith("USE_COUNTER2_"):
+        return "UseCounterWorker" if name.endswith("_WORKER") else "UseCounter"
+    return None
+
+
 def main(output, *filenames):
     # Print header.
     print(banner, file=output)
     print(header, file=output)
 
     # Load the histograms.
     try:
         all_histograms = list(parse_histograms.from_files(filenames))
     except ParserError as ex:
         print("\nError processing histograms:\n" + str(ex) + "\n")
         sys.exit(1)
 
-    groups = itertools.groupby(all_histograms,
-                               lambda h: h.name().startswith("USE_COUNTER2_"))
+    groups = itertools.groupby(all_histograms, get_histogram_typename)
 
     # Print the histogram enums.
-    # Note that parse_histograms.py guarantees that all of the USE_COUNTER2_*
-    # histograms are defined in a contiguous block.  We therefore assume
-    # that there's at most one group for which use_counter_group is true.
+    # Note that parse_histograms.py guarantees that all of the
+    # USE_COUNTER2_*_WORKER and USE_COUNTER2_* histograms are both defined in a
+    # contiguous block.
     print("enum HistogramID : uint32_t {", file=output)
-    seen_use_counters = False
-    for (use_counter_group, histograms) in groups:
-        if use_counter_group:
-            seen_use_counters = True
-
-        # The HistogramDUMMY* enum variables are used to make the computation
-        # of Histogram{First,Last}UseCounter easier.  Otherwise, we'd have to
-        # special case the first and last histogram in the group.
-        if use_counter_group:
-            print("  HistogramFirstUseCounter,", file=output)
-            print("  HistogramDUMMY1 = HistogramFirstUseCounter - 1,", file=output)
+    seen_group_types = {"UseCounter": False, "UseCounterWorker": False}
+    for (group_type, histograms) in groups:
+        if group_type is not None:
+            assert isinstance(group_type, basestring)
+            assert group_type in seen_group_types.keys()
+            assert not seen_group_types[group_type]
+            seen_group_types[group_type] = True
+            # The Histogram*DUMMY enum variables are used to make the computation
+            # of Histogram{First,Last}* easier.  Otherwise, we'd have to special
+            # case the first and last histogram in the group.
+            print("  HistogramFirst%s," % group_type, file=output)
+            print("  Histogram{0}DUMMY1 = HistogramFirst{0} - 1,".format(group_type), file=output)
 
         for histogram in histograms:
             if histogram.record_on_os(buildconfig.substs["OS_TARGET"]):
                 print("  %s," % histogram.name(), file=output)
 
-        if use_counter_group:
-            print("  HistogramDUMMY2,", file=output)
-            print("  HistogramLastUseCounter = HistogramDUMMY2 - 1,", file=output)
+        if group_type is not None:
+            assert isinstance(group_type, basestring)
+            print("  Histogram%sDUMMY2," % group_type, file=output)
+            print("  HistogramLast{0} = Histogram{0}DUMMY2 - 1,".format(group_type), file=output)
 
     print("  HistogramCount,", file=output)
-    if seen_use_counters:
-        print("  HistogramUseCounterCount = HistogramLastUseCounter -"
-              " HistogramFirstUseCounter + 1", file=output)
-    else:
-        print("  HistogramFirstUseCounter = 0,", file=output)
-        print("  HistogramLastUseCounter = 0,", file=output)
-        print("  HistogramUseCounterCount = 0", file=output)
+
+    for (key, value) in seen_group_types.items():
+        if value:
+            print("  Histogram{0}Count = HistogramLast{0} - HistogramFirst{0} + 1,"
+                  .format(key), file=output)
+        else:
+            print("  HistogramFirst%s = 0," % key, file=output)
+            print("  HistogramLast%s = 0," % key, file=output)
+            print("  Histogram%sCount = 0," % key, file=output)
+
     print("};", file=output)
 
     # Write categorical label enums.
     categorical = filter(lambda h: h.kind() == "categorical", all_histograms)
     categorical = filter(lambda h: h.record_on_os(buildconfig.substs["OS_TARGET"]), categorical)
     enums = [("LABELS_" + h.name(), h.labels(), h.name()) for h in categorical]
     for name, labels, _ in enums:
         print("\nenum class %s : uint32_t {" % name, file=output)

--- a/toolkit/components/telemetry/build_scripts/mozparsers/parse_histograms.py
+++ b/toolkit/components/telemetry/build_scripts/mozparsers/parse_histograms.py
@@ -720,16 +720,20 @@ def from_json(filename, strict_type_chec
             ParserError("error parsing histograms in %s: %s" % (filename, e.message)).handle_now()
     return histograms
 
 
 def from_UseCounters_conf(filename, strict_type_checks):
     return usecounters.generate_histograms(filename)
 
 
+def from_UseCountersWorker_conf(filename, strict_type_checks):
+    return usecounters.generate_histograms(filename, True)
+
+
 def from_nsDeprecatedOperationList(filename, strict_type_checks):
     operation_regex = re.compile('^DEPRECATED_OPERATION\\(([^)]+)\\)')
     histograms = collections.OrderedDict()
 
     with open(filename, 'r') as f:
         for line in f:
             match = operation_regex.search(line)
             if not match:
@@ -823,16 +827,18 @@ FILENAME_PARSERS = [
 ]
 
 # Similarly to the dance above with buildconfig, usecounters may not be
 # available, so handle that gracefully.
 try:
     import usecounters
 
     FILENAME_PARSERS.append(lambda x: from_UseCounters_conf if x == 'UseCounters.conf' else None)
+    FILENAME_PARSERS.append(
+        lambda x: from_UseCountersWorker_conf if x == 'UseCountersWorker.conf' else None)
 except ImportError:
     pass
 
 
 def from_files(filenames, strict_type_checks=True):
     """Return an iterator that provides a sequence of Histograms for
 the histograms defined in filenames.
     """
@@ -859,27 +865,36 @@ the histograms defined in filenames.
         if not isinstance(histograms, OrderedDict):
             ParserError("Histogram parser did not provide an OrderedDict.").handle_now()
 
         for (name, definition) in histograms.iteritems():
             if name in all_histograms:
                 ParserError('Duplicate histogram name "%s".' % name).handle_later()
             all_histograms[name] = definition
 
-    # We require that all USE_COUNTER2_* histograms be defined in a contiguous
+    def check_continuity(iterable, filter_function, name):
+        indices = filter(filter_function, enumerate(iterable.iterkeys()))
+        if indices:
+            lower_bound = indices[0][0]
+            upper_bound = indices[-1][0]
+            n_counters = upper_bound - lower_bound + 1
+            if n_counters != len(indices):
+                ParserError("Histograms %s must be defined in a contiguous block." %
+                            name).handle_later()
+
+    # We require that all USE_COUNTER2_*_WORKER histograms be defined in a contiguous
     # block.
-    use_counter_indices = filter(lambda x: x[1].startswith("USE_COUNTER2_"),
-                                 enumerate(all_histograms.iterkeys()))
-    if use_counter_indices:
-        lower_bound = use_counter_indices[0][0]
-        upper_bound = use_counter_indices[-1][0]
-        n_counters = upper_bound - lower_bound + 1
-        if n_counters != len(use_counter_indices):
-            ParserError("Use counter histograms must be defined in a contiguous block."
-                        ).handle_later()
+    check_continuity(all_histograms,
+                     lambda x: x[1].startswith("USE_COUNTER2_") and x[1].endswith("_WORKER"),
+                     "use counter worker")
+    # And all other USE_COUNTER2_* histograms be defined in a contiguous
+    # block.
+    check_continuity(all_histograms,
+                     lambda x: x[1].startswith("USE_COUNTER2_") and not x[1].endswith("_WORKER"),
+                     "use counter")
 
     # Check that histograms that were removed from Histograms.json etc.
     # are also removed from the allowlists.
     if allowlists is not None:
         all_allowlist_entries = itertools.chain.from_iterable(allowlists.itervalues())
         orphaned = set(all_allowlist_entries) - set(all_histograms.keys())
         if len(orphaned) > 0:
             msg = 'The following entries are orphaned and should be removed from ' \

--- a/toolkit/components/telemetry/histogram-allowlists.json
+++ b/toolkit/components/telemetry/histogram-allowlists.json
@@ -1183,16 +1183,17 @@
     "CSP_DOCUMENTS_COUNT",
     "CSP_UNSAFE_EVAL_DOCUMENTS_COUNT",
     "CSP_UNSAFE_INLINE_DOCUMENTS_COUNT",
     "CYCLE_COLLECTOR_OOM",
     "CYCLE_COLLECTOR_WORKER_OOM",
     "D3D11_COMPOSITING_FAILURE_ID",
     "D3D11_SYNC_HANDLE_FAILURE",
     "DEDICATED_WORKER_SPAWN_GETS_QUEUED",
+    "DEDICATED_WORKER_DESTROYED",
     "DEFECTIVE_PERMISSIONS_SQL_REMOVED",
     "DENIED_TRANSLATION_OFFERS",
     "DEVTOOLS_ABOUTDEBUGGING_OPENED_COUNT",
     "DEVTOOLS_ANIMATIONINSPECTOR_OPENED_COUNT",
     "DEVTOOLS_BROWSERCONSOLE_OPENED_COUNT",
     "DEVTOOLS_COMPUTEDVIEW_OPENED_COUNT",
     "DEVTOOLS_CUSTOM_OPENED_COUNT",
     "DEVTOOLS_DOM_OPENED_COUNT",
@@ -1254,17 +1255,19 @@
     "SEARCH_SERVICE_US_COUNTRY_MISMATCHED_TIMEZONE",
     "SEARCH_SERVICE_US_TIMEZONE_MISMATCHED_COUNTRY",
     "SERVICE_WORKER_CONTROLLED_DOCUMENTS",
     "SERVICE_WORKER_REGISTRATIONS",
     "SERVICE_WORKER_SPAWN_ATTEMPTS",
     "SERVICE_WORKER_SPAWN_GETS_QUEUED",
     "SERVICE_WORKER_UPDATED",
     "SERVICE_WORKER_WAS_SPAWNED",
+    "SERVICE_WORKER_DESTROYED",
     "SHARED_WORKER_SPAWN_GETS_QUEUED",
+    "SHARED_WORKER_DESTROYED",
     "SHOULD_AUTO_DETECT_LANGUAGE",
     "SHOULD_TRANSLATION_UI_APPEAR",
     "SLOW_SCRIPT_NOTICE_COUNT",
     "SLOW_SCRIPT_PAGE_COUNT",
     "STARTUP_CRASH_DETECTED",
     "STORAGE_SYNC_REMOVE_OPS",
     "SUBPROCESS_ABNORMAL_ABORT",
     "SUBPROCESS_CRASHES_WITH_DUMP",

--- a/toolkit/components/telemetry/moz.build
+++ b/toolkit/components/telemetry/moz.build
@@ -138,16 +138,17 @@ PYTHON_UNITTEST_MANIFESTS += [
 
 # Generate histogram files.
 histogram_files = [
     'Histograms.json',
     '/dom/base/UseCounters.conf',
     '/dom/base/nsDeprecatedOperationList.h',
     '!/layout/style/ServoCSSPropList.py',
     '/servo/components/style/properties/counted_unknown_properties.py',
+    '/dom/base/UseCountersWorker.conf',
 ]
 if CONFIG['MOZ_TELEMETRY_EXTRA_HISTOGRAM_FILES']:
     histogram_files.extend(CONFIG['MOZ_TELEMETRY_EXTRA_HISTOGRAM_FILES'])
 
 GeneratedFile('TelemetryHistogramData.inc',
               script='build_scripts/gen_histogram_data.py',
               inputs=histogram_files)
 GeneratedFile('TelemetryHistogramEnums.h',