new file mode 100644
--- /dev/null
+++ b/js/src/devtools/gc-ubench/harness.js
@@ -0,0 +1,377 @@
+// Per-frame time sampling infra. Also GC'd: hopefully will not perturb things too badly.
+var numSamples = 500;
+var delays = new Array(numSamples);
+var sampleIndex = 0;
+var sampleTime = 16; // ms
+var gHistogram = new Map(); // {ms: count}
+
+// Draw state.
+var stopped = 0;
+var start;
+var prev;
+var ctx;
+
+// Current test state.
+var garbagePerFrame = undefined;
+var garbageTotal = undefined;
+var activeTest = undefined;
+var testDuration = undefined; // ms
+var testState = 'idle';  // One of 'idle' or 'running'.
+var testStart = undefined; // ms
+var testQueue = [];
+
+function xpos(index)
+{
+    return index * 2;
+}
+
+function ypos(delay)
+{
+    var r = 525 - Math.log(delay) * 64;
+    if (r < 5) return 5;
+    return r;
+}
+
+function drawHBar(delay, color, label)
+{
+    ctx.fillStyle = color;
+    ctx.strokeStyle = color;
+    ctx.fillText(label, xpos(numSamples) + 4, ypos(delay) + 3);
+
+    ctx.beginPath();
+    ctx.moveTo(xpos(0), ypos(delay));
+    ctx.lineTo(xpos(numSamples), ypos(delay));
+    ctx.stroke();
+    ctx.strokeStyle = 'rgb(0,0,0)';
+    ctx.fillStyle = 'rgb(0,0,0)';
+}
+
+function drawScale(delay)
+{
+    drawHBar(delay, 'rgb(150,150,150)', `${delay}ms`);
+}
+
+function draw60fps() {
+    drawHBar(1000/60, '#00cf61', '60fps');
+}
+
+function draw30fps() {
+    drawHBar(1000/30, '#cf0061', '30fps');
+}
+
+function drawGraph()
+{
+    ctx.clearRect(0, 0, 1100, 550);
+
+    drawScale(10);
+    draw60fps();
+    drawScale(20);
+    drawScale(30);
+    draw30fps();
+    drawScale(50);
+    drawScale(100);
+    drawScale(200);
+    drawScale(400);
+    drawScale(800);
+
+    var worst = 0, worstpos = 0;
+    ctx.beginPath();
+    for (var i = 0; i < numSamples; i++) {
+        ctx.lineTo(xpos(i), ypos(delays[i]));
+        if (delays[i] >= worst) {
+            worst = delays[i];
+            worstpos = i;
+        }
+    }
+    ctx.stroke();
+
+    ctx.fillStyle = 'rgb(255,0,0)';
+    if (worst)
+        ctx.fillText(''+worst+'ms', xpos(worstpos) - 10, ypos(worst) - 14);
+
+    ctx.beginPath();
+    var where = sampleIndex % numSamples;
+    ctx.arc(xpos(where), ypos(delays[where]), 5, 0, Math.PI*2, true);
+    ctx.fill();
+    ctx.fillStyle = 'rgb(0,0,0)';
+
+    ctx.fillText('Time', 550, 420);
+    ctx.save();
+    ctx.rotate(Math.PI/2);
+    ctx.fillText('Pause between frames (log scale)', 150, -1060);
+    ctx.restore();
+}
+
+function stopstart()
+{
+    if (stopped) {
+        window.requestAnimationFrame(handler);
+        prev = performance.now();
+        start += prev - stopped;
+        document.getElementById('stop').value = 'Pause';
+        stopped = 0;
+    } else {
+        document.getElementById('stop').value = 'Resume';
+        stopped = performance.now();
+    }
+}
+
+function handler(timestamp)
+{
+    if (stopped)
+        return;
+
+    if (testState === 'running' && (timestamp - testStart) > testDuration)
+        end_test(timestamp);
+
+    activeTest.makeGarbage(garbagePerFrame);
+
+    var elt = document.getElementById('data');
+    var delay = timestamp - prev;
+    prev = timestamp;
+
+    // Take the histogram at 10us intervals so that we have enough resolution to capture.
+    // a 16.66[666] target with adequate accuracy.
+    update_histogram(gHistogram, Math.round(delay * 100));
+
+    var t = timestamp - start;
+    var newIndex = Math.round(t / sampleTime);
+    while (sampleIndex < newIndex) {
+        sampleIndex++;
+        delays[sampleIndex % numSamples] = delay;
+    }
+
+    drawGraph();
+    window.requestAnimationFrame(handler);
+}
+
+function update_histogram(histogram, delay)
+{
+    var current = histogram.has(delay) ? histogram.get(delay) : 0;
+    histogram.set(delay, ++current);
+}
+
+function reset_draw_state()
+{
+    for (var i = 0; i < numSamples; i++)
+        delays[i] = 0;
+    start = prev = performance.now();
+    sampleIndex = 0;
+}
+
+function onunload()
+{
+    if (activeTest)
+        activeTest.unload();
+    activeTest = undefined;
+}
+
+function onload()
+{
+    // Load initial test duration.
+    duration_changed();
+
+    // Load initial garbage size.
+    garbage_total_changed();
+    garbage_per_frame_changed();
+
+    // Populate the test selection dropdown.
+    var select = document.getElementById("test-selection");
+    for (var [name, test] of tests) {
+        test.name = name;
+        var option = document.createElement("option");
+        option.id = name;
+        option.text = name;
+        option.title = test.description;
+        select.add(option);
+    }
+
+    // Load the initial test.
+    activeTest = tests.get('noAllocation');
+    activeTest.load(garbageTotal);
+
+    // Polyfill rAF.
+    var requestAnimationFrame =
+        window.requestAnimationFrame || window.mozRequestAnimationFrame ||
+        window.webkitRequestAnimationFrame || window.msRequestAnimationFrame;
+    window.requestAnimationFrame = requestAnimationFrame;
+
+    // Acquire our canvas.
+    var canvas = document.getElementById('graph');
+    ctx = canvas.getContext('2d');
+
+    // Start drawing.
+    reset_draw_state();
+    window.requestAnimationFrame(handler);
+}
+
+function run_one_test()
+{
+    start_test_cycle([activeTest.name]);
+}
+
+function run_all_tests()
+{
+    start_test_cycle(tests.keys());
+}
+
+function start_test_cycle(tests_to_run)
+{
+    // Convert from an iterable to an array for pop.
+    testQueue = [];
+    for (var key of tests_to_run)
+        testQueue.push(key);
+    testState = 'running';
+    testStart = performance.now();
+    gHistogram.clear();
+
+    change_active_test(testQueue.pop());
+    console.log(`Running test: ${activeTest.name}`);
+    reset_draw_state();
+}
+
+function end_test(timestamp)
+{
+    report_test_result(activeTest, gHistogram);
+    gHistogram.clear();
+    console.log(`Ending test ${activeTest.name}`);
+    if (testQueue.length) {
+        change_active_test(testQueue.pop());
+        console.log(`Running test: ${activeTest.name}`);
+        testStart = timestamp;
+    } else {
+        testState = 'idle';
+        testStart = 0;
+    }
+    reset_draw_state();
+}
+
+function report_test_result(test, histogram)
+{
+    var resultList = document.getElementById('results-display');
+    var resultElem = document.createElement("div");
+    var score = compute_test_score(histogram);
+    var sparks = compute_test_spark_histogram(histogram);
+    resultElem.innerHTML = `${score} ms/s : ${sparks} : ${test.name} - ${test.description}`;
+    resultList.appendChild(resultElem);
+}
+
+// Compute a score based on the total ms we missed frames by per second.
+function compute_test_score(histogram)
+{
+    var score = 0;
+    for (var [delay, count] of histogram) {
+        delay = delay / 100;
+        score += Math.abs((delay - 16.66) * count);
+    }
+    score = score / (testDuration / 1000);
+    return Math.round(score * 1000) / 1000;
+}
+
+// Build a spark-lines histogram for the test results to show with the aggregate score.
+function compute_test_spark_histogram(histogram)
+{
+    var ranges = [
+        [-99999999, 16.6],
+        [16.6, 16.8],
+        [16.8, 25],
+        [25, 33.4],
+        [33.4, 60],
+        [60, 100],
+        [100, 300],
+        [300, 99999999],
+    ];
+    var rescaled = new Map();
+    for (var [delay, count] of histogram) {
+        delay = delay / 100;
+        for (var i = 0; i < ranges.length; ++i) {
+            var low = ranges[i][0];
+            var high = ranges[i][1];
+            if (low <= delay && delay < high) {
+                update_histogram(rescaled, i);
+                break;
+            }
+        }
+    }
+    var total = 0;
+    for (var [i, count] of rescaled)
+        total += count;
+    var sparks = "▁▂▃▄▅▆▇█";
+    var colors = ['#aaaa00', '#007700', '#dd0000', '#ff0000',
+                  '#ff0000', '#ff0000', '#ff0000', '#ff0000'];
+    var line = "";
+    for (var i = 0; i < ranges.length; ++i) {
+        var amt = rescaled.has(i) ? rescaled.get(i) : 0;
+        var spark = sparks.charAt(parseInt(amt/total*8));
+        line += `<span style="color:${colors[i]}">${spark}</span>`;
+    }
+    return line;
+}
+
+function reload_active_test()
+{
+    activeTest.unload();
+    activeTest.load(garbageTotal);
+}
+
+function change_active_test(new_test_name)
+{
+    activeTest.unload();
+    activeTest = tests.get(new_test_name);
+    activeTest.load(garbageTotal);
+}
+
+function duration_changed()
+{
+    var durationInput = document.getElementById('test-duration');
+    testDuration = parseInt(durationInput.value) * 1000;
+    console.log(`Updated test duration to: ${testDuration / 1000} seconds`);
+}
+
+function testchanged()
+{
+    var select = document.getElementById("test-selection");
+    console.log(`Switching to test: ${select.value}`);
+    change_active_test(select.value);
+    gHistogram.clear();
+    reset_draw_state();
+}
+
+function parse_units(v)
+{
+    if (v.length == 0)
+        return NaN;
+    var lastChar = v[v.length - 1].toLowerCase();
+    if (!isNaN(parseFloat(lastChar)))
+        return parseFloat(v);
+    var units = parseFloat(v.substr(0, v.length - 1));
+    if (lastChar == "k")
+        return units * 1e3;
+    if (lastChar == "m")
+        return units * 1e6;
+    if (lastChar == "g")
+        return units * 1e9;
+    return NaN;
+}
+
+function garbage_total_changed()
+{
+    var value = parse_units(document.getElementById('garbage-total').value);
+    if (isNaN(value))
+        return;
+    garbageTotal = value;
+    console.log(`Updated garbage-total to ${garbageTotal} items`);
+    if (activeTest)
+        reload_active_test();
+    gHistogram.clear();
+    reset_draw_state();
+}
+
+function garbage_per_frame_changed()
+{
+    var value = parse_units(document.getElementById('garbage-per-frame').value);
+    if (isNaN(value))
+        return;
+    garbagePerFrame = value;
+    console.log(`Updated garbage-per-frame to ${garbagePerFrame} items`);
+}

--- a/js/src/devtools/gc-ubench/index.html
+++ b/js/src/devtools/gc-ubench/index.html
@@ -1,391 +1,27 @@
 <html>
 <head>
   <title>GC uBench</title>
   <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
-</head>
-<body onload="onload()" onunload="onunload()">
-
-<!-- Include benchmark modules. -->
-<script>var tests = new Map();</script>
-<script src="benchmarks/noAllocation.js"></script>
-<script src="benchmarks/globalArrayNewObject.js"></script>
-<script src="benchmarks/globalArrayArrayLiteral.js"></script>
-<script src="benchmarks/globalArrayLargeArray.js"></script>
-<script src="benchmarks/globalArrayObjectLiteral.js"></script>
-<script src="benchmarks/globalArrayReallocArray.js"></script>
-
-<!-- Harness implementation. -->
-<script>
-// Per-frame time sampling infra. Also GC'd: hopefully will not perturb things too badly.
-var numSamples = 500;
-var delays = new Array(numSamples);
-var sampleIndex = 0;
-var sampleTime = 16; // ms
-var gHistogram = new Map(); // {ms: count}
-
-// Draw state.
-var stopped = 0;
-var start;
-var prev;
-var ctx;
-
-// Current test state.
-var garbagePerFrame = undefined;
-var garbageTotal = undefined;
-var activeTest = undefined;
-var testDuration = undefined; // ms
-var testState = 'idle';  // One of 'idle' or 'running'.
-var testStart = undefined; // ms
-var testQueue = [];
-
-function xpos(index)
-{
-    return index * 2;
-}
-
-function ypos(delay)
-{
-    var r = 525 - Math.log(delay) * 64;
-    if (r < 5) return 5;
-    return r;
-}
-
-function drawHBar(delay, color, label)
-{
-    ctx.fillStyle = color;
-    ctx.strokeStyle = color;
-    ctx.fillText(label, xpos(numSamples) + 4, ypos(delay) + 3);
-
-    ctx.beginPath();
-    ctx.moveTo(xpos(0), ypos(delay));
-    ctx.lineTo(xpos(numSamples), ypos(delay));
-    ctx.stroke();
-    ctx.strokeStyle = 'rgb(0,0,0)';
-    ctx.fillStyle = 'rgb(0,0,0)';
-}
-
-function drawScale(delay)
-{
-    drawHBar(delay, 'rgb(150,150,150)', `${delay}ms`);
-}
-
-function draw60fps() {
-    drawHBar(1000/60, '#00cf61', '60fps');
-}
-
-function draw30fps() {
-    drawHBar(1000/30, '#cf0061', '30fps');
-}
-
-function drawGraph()
-{
-    ctx.clearRect(0, 0, 1100, 550);
-
-    drawScale(10);
-    draw60fps();
-    drawScale(20);
-    drawScale(30);
-    draw30fps();
-    drawScale(50);
-    drawScale(100);
-    drawScale(200);
-    drawScale(400);
-    drawScale(800);
-
-    var worst = 0, worstpos = 0;
-    ctx.beginPath();
-    for (var i = 0; i < numSamples; i++) {
-        ctx.lineTo(xpos(i), ypos(delays[i]));
-        if (delays[i] >= worst) {
-            worst = delays[i];
-            worstpos = i;
-        }
-    }
-    ctx.stroke();
-
-    ctx.fillStyle = 'rgb(255,0,0)';
-    if (worst)
-        ctx.fillText(''+worst+'ms', xpos(worstpos) - 10, ypos(worst) - 14);
-
-    ctx.beginPath();
-    var where = sampleIndex % numSamples;
-    ctx.arc(xpos(where), ypos(delays[where]), 5, 0, Math.PI*2, true);
-    ctx.fill();
-    ctx.fillStyle = 'rgb(0,0,0)';
-
-    ctx.fillText('Time', 550, 420);
-    ctx.save();
-    ctx.rotate(Math.PI/2);
-    ctx.fillText('Pause between frames (log scale)', 150, -1060);
-    ctx.restore();
-}
-
-function stopstart()
-{
-    if (stopped) {
-        window.requestAnimationFrame(handler);
-        prev = performance.now();
-        start += prev - stopped;
-        document.getElementById('stop').value = 'Pause';
-        stopped = 0;
-    } else {
-        document.getElementById('stop').value = 'Resume';
-        stopped = performance.now();
-    }
-}
-
-function handler(timestamp)
-{
-    if (stopped)
-        return;
-
-    if (testState === 'running' && (timestamp - testStart) > testDuration)
-        end_test(timestamp);
-
-    activeTest.makeGarbage(garbagePerFrame);
-
-    var elt = document.getElementById('data');
-    var delay = timestamp - prev;
-    prev = timestamp;
-
-    // Take the histogram at 10us intervals so that we have enough resolution to capture.
-    // a 16.66[666] target with adequate accuracy.
-    update_histogram(gHistogram, Math.round(delay * 100));
-
-    var t = timestamp - start;
-    var newIndex = Math.round(t / sampleTime);
-    while (sampleIndex < newIndex) {
-        sampleIndex++;
-        delays[sampleIndex % numSamples] = delay;
-    }
-
-    drawGraph();
-    window.requestAnimationFrame(handler);
-}
-
-function update_histogram(histogram, delay)
-{
-    var current = histogram.has(delay) ? histogram.get(delay) : 0;
-    histogram.set(delay, ++current);
-}
-
-function reset_draw_state()
-{
-    for (var i = 0; i < numSamples; i++)
-        delays[i] = 0;
-    start = prev = performance.now();
-    sampleIndex = 0;
-}
-
-function onunload()
-{
-    activeTest.unload();
-    activeTest = undefined;
-}
-
-function onload()
-{
-    // Load initial test duration.
-    duration_changed();
-
-    // Load initial garbage size.
-    garbage_total_changed();
-    garbage_per_frame_changed();
 
-    // Populate the test selection dropdown.
-    var select = document.getElementById("test-selection");
-    for (var [name, test] of tests) {
-        test.name = name;
-        var option = document.createElement("option");
-        option.id = name;
-        option.text = name;
-        option.title = test.description;
-        select.add(option);
-    }
-
-    // Load the initial test.
-    activeTest = tests.get('noAllocation');
-    activeTest.load(garbageTotal);
-
-    // Polyfill rAF.
-    var requestAnimationFrame =
-        window.requestAnimationFrame || window.mozRequestAnimationFrame ||
-        window.webkitRequestAnimationFrame || window.msRequestAnimationFrame;
-    window.requestAnimationFrame = requestAnimationFrame;
-
-    // Acquire our canvas.
-    var canvas = document.getElementById('graph');
-    ctx = canvas.getContext('2d');
-
-    // Start drawing.
-    reset_draw_state();
-    window.requestAnimationFrame(handler);
-}
-
-function run_one_test()
-{
-    start_test_cycle([activeTest.name]);
-}
-
-function run_all_tests()
-{
-    start_test_cycle(tests.keys());
-}
-
-function start_test_cycle(tests_to_run)
-{
-    // Convert from an iterable to an array for pop.
-    testQueue = [];
-    for (var key of tests_to_run)
-        testQueue.push(key);
-    testState = 'running';
-    testStart = performance.now();
-    gHistogram.clear();
-
-    change_active_test(testQueue.pop());
-    console.log(`Running test: ${activeTest.name}`);
-    reset_draw_state();
-}
-
-function end_test(timestamp)
-{
-    report_test_result(activeTest, gHistogram);
-    gHistogram.clear();
-    console.log(`Ending test ${activeTest.name}`);
-    if (testQueue.length) {
-        change_active_test(testQueue.pop());
-        console.log(`Running test: ${activeTest.name}`);
-        testStart = timestamp;
-    } else {
-        testState = 'idle';
-        testStart = 0;
-    }
-    reset_draw_state();
-}
-
-function report_test_result(test, histogram)
-{
-    var resultList = document.getElementById('results-display');
-    var resultElem = document.createElement("div");
-    var score = compute_test_score(histogram);
-    var sparks = compute_test_spark_histogram(histogram);
-    resultElem.innerHTML = `${score} ms/s : ${sparks} : ${test.name} - ${test.description}`;
-    resultList.appendChild(resultElem);
-}
-
-// Compute a score based on the total ms we missed frames by per second.
-function compute_test_score(histogram)
-{
-    var score = 0;
-    for (var [delay, count] of histogram) {
-        delay = delay / 100;
-        score += Math.abs((delay - 16.66) * count);
-    }
-    score = score / (testDuration / 1000);
-    return Math.round(score * 1000) / 1000;
-}
+  <!-- Include benchmark modules. -->
+  <script>var tests = new Map();</script>
+  <script src="benchmarks/noAllocation.js"></script>
+  <script src="benchmarks/globalArrayNewObject.js"></script>
+  <script src="benchmarks/globalArrayArrayLiteral.js"></script>
+  <script src="benchmarks/globalArrayLargeArray.js"></script>
+  <script src="benchmarks/globalArrayObjectLiteral.js"></script>
+  <script src="benchmarks/globalArrayReallocArray.js"></script>
 
-// Build a spark-lines histogram for the test results to show with the aggregate score.
-function compute_test_spark_histogram(histogram)
-{
-    var ranges = [
-        [-99999999, 16.6],
-        [16.6, 16.8],
-        [16.8, 25],
-        [25, 33.4],
-        [33.4, 60],
-        [60, 100],
-        [100, 300],
-        [300, 99999999],
-    ];
-    var rescaled = new Map();
-    for (var [delay, count] of histogram) {
-        delay = delay / 100;
-        for (var i = 0; i < ranges.length; ++i) {
-            var low = ranges[i][0];
-            var high = ranges[i][1];
-            if (low <= delay && delay < high) {
-                update_histogram(rescaled, i);
-                break;
-            }
-        }
-    }
-    var total = 0;
-    for (var [i, count] of rescaled)
-        total += count;
-    var sparks = "▁▂▃▄▅▆▇█";
-    var colors = ['#aaaa00', '#007700', '#dd0000', '#ff0000',
-                  '#ff0000', '#ff0000', '#ff0000', '#ff0000'];
-    var line = "";
-    for (var i = 0; i < ranges.length; ++i) {
-        var amt = rescaled.has(i) ? rescaled.get(i) : 0;
-        var spark = sparks.charAt(parseInt(amt/total*8));
-        line += `<span style="color:${colors[i]}">${spark}</span>`;
-    }
-    return line;
-}
-
-function reload_active_test()
-{
-    activeTest.unload();
-    activeTest.load(garbageTotal);
-}
+  <script src="harness.js"></script>
 
-function change_active_test(new_test_name)
-{
-    activeTest.unload();
-    activeTest = tests.get(new_test_name);
-    activeTest.load(garbageTotal);
-}
-
-function duration_changed()
-{
-    var durationInput = document.getElementById('test-duration');
-    testDuration = parseInt(durationInput.value) * 1000;
-    console.log(`Updated test duration to: ${testDuration / 1000} seconds`);
-}
-
-function testchanged()
-{
-    var select = document.getElementById("test-selection");
-    console.log(`Switching to test: ${select.value}`);
-    change_active_test(select.value);
-    gHistogram.clear();
-    reset_draw_state();
-}
+</head>
 
-function garbage_total_changed()
-{
-    var mult = parseInt(document.getElementById('garbage-total-unit').value);
-    var base = parseInt(document.getElementById('garbage-total-size').value);
-    if (isNaN(mult) || isNaN(base))
-        return;
-    garbageTotal = base * mult;
-    console.log(`Updated garbage-total to ${garbageTotal} items`);
-    if (activeTest)
-        reload_active_test();
-    gHistogram.clear();
-    reset_draw_state();
-}
-
-function garbage_per_frame_changed()
-{
-    var mult = parseInt(document.getElementById('garbage-per-frame-unit').value);
-    var base = parseInt(document.getElementById('garbage-per-frame-size').value);
-    if (isNaN(mult) || isNaN(base))
-        return;
-    garbagePerFrame = base * mult;
-    console.log(`Updated garbage-per-frame to ${garbagePerFrame} items`);
-}
-</script>
-
-<script>
-</script>
+<body onload="onload()" onunload="onunload()">
 
 <canvas id="graph" width="1080" height="550" style="padding-left:10px"></canvas>
 
 <div>
     <input type="button" id="stop" value="Pause" onclick="stopstart()"></input>
 </div>
 
 <div>
@@ -396,33 +32,23 @@ function garbage_per_frame_changed()
 
 <div>
     Currently running test:
     <select id="test-selection" required onchange="testchanged()"></select>
 </div>
 
 <div>
     Garbage items per frame:
-    <input type="text" id="garbage-per-frame-size" size=5 value="8"
+    <input type="text" id="garbage-per-frame" size=5 value="8K"
            oninput="garbage_per_frame_changed()"></input>
-    <select id="garbage-per-frame-unit" required>
-        <option value="1"></option>
-        <option value="1000" selected="selected">K</option>
-        <option value="1000000">M</option>
-    </select>
 </div>
 <div>
     Garbage heap size in items:
-    <input type="text" id="garbage-total-size" size=5 value="8"
+    <input type="text" id="garbage-total" size=5 value="8M"
            oninput="garbage_total_changed()"></input>
-    <select id="garbage-total-unit" required>
-        <option value="1"></option>
-        <option value="1000">K</option>
-        <option value="1000000" selected="selected">M</option>
-    </select>
 </div>
 
 <div id="results-Area">
     Test Results:
     <div id="results-display" style="padding-left: 10px; border: 1px solid black;"></div>
 </div>
 
 </body>