--- a/modules/plugin/test/testplugin/README
+++ b/modules/plugin/test/testplugin/README
@@ -166,16 +166,20 @@ for windowed plugins too (Silverlight de
 * getPaintCount()
 Returns the number of times this plugin instance has processed a paint request.
 This can be used to detect whether painting has happened in a plugin's
 window.
 
 * getWidthAtLastPaint()
 Returns the window width that was current when the plugin last painted.
 
+* setInvalidateDuringPaint(value)
+When value is true, every time the plugin paints, it will invalidate
+itself *during the paint* using NPN_Invalidate.
+
 == Plugin geometry ==
 
 The test plugin supports the following scriptable methods:
 
 * getEdge(edge)
 Returns the integer screen pixel coordinate of an edge of the plugin's
 area:
 -- edge=0: returns left edge coordinate

--- a/modules/plugin/test/testplugin/nptest.cpp
+++ b/modules/plugin/test/testplugin/nptest.cpp
@@ -137,16 +137,17 @@ static bool getClipRegionRectCount(NPObj
 static bool getClipRegionRectEdge(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool startWatchingInstanceCount(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool getInstanceCount(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool stopWatchingInstanceCount(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool getLastMouseX(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool getLastMouseY(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool getPaintCount(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool getWidthAtLastPaint(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
+static bool setInvalidateDuringPaint(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool getError(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool doInternalConsistencyCheck(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool setColor(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool throwExceptionNextInvoke(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool convertPointX(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool convertPointY(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool streamTest(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
 static bool crashPlugin(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result);
@@ -187,16 +188,17 @@ static const NPUTF8* sPluginMethodIdenti
   "getClipRegionRectEdge",
   "startWatchingInstanceCount",
   "getInstanceCount",
   "stopWatchingInstanceCount",
   "getLastMouseX",
   "getLastMouseY",
   "getPaintCount",
   "getWidthAtLastPaint",
+  "setInvalidateDuringPaint",
   "getError",
   "doInternalConsistencyCheck",
   "setColor",
   "throwExceptionNextInvoke",
   "convertPointX",
   "convertPointY",
   "streamTest",
   "crash",
@@ -238,16 +240,17 @@ static const ScriptableFunction sPluginM
   getClipRegionRectEdge,
   startWatchingInstanceCount,
   getInstanceCount,
   stopWatchingInstanceCount,
   getLastMouseX,
   getLastMouseY,
   getPaintCount,
   getWidthAtLastPaint,
+  setInvalidateDuringPaint,
   getError,
   doInternalConsistencyCheck,
   setColor,
   throwExceptionNextInvoke,
   convertPointX,
   convertPointY,
   streamTest,
   crashPlugin,
@@ -684,16 +687,17 @@ NPP_New(NPMIMEType pluginType, NPP insta
   instanceData->streamBuf = NULL;
   instanceData->streamBufSize = 0;
   instanceData->fileBuf = NULL;
   instanceData->fileBufSize = 0;
   instanceData->throwOnNextInvoke = false;
   instanceData->testrange = NULL;
   instanceData->hasWidget = false;
   instanceData->npnNewStream = false;
+  instanceData->invalidateDuringPaint = false;
   instanceData->writeCount = 0;
   instanceData->writeReadyCount = 0;
   memset(&instanceData->window, 0, sizeof(instanceData->window));
   instanceData->crashOnDestroy = false;
   instanceData->cleanupWidget = true; // only used by nptest_gtk
   instanceData->topLevelWindowActivationState = ACTIVATION_STATE_UNKNOWN;
   instanceData->topLevelWindowActivationEventCount = 0;
   instanceData->focusState = ACTIVATION_STATE_UNKNOWN;
@@ -2123,16 +2127,32 @@ getWidthAtLastPaint(NPObject* npobj, con
 
   NPP npp = static_cast<TestNPObject*>(npobj)->npp;
   InstanceData* id = static_cast<InstanceData*>(npp->pdata);
   INT32_TO_NPVARIANT(id->widthAtLastPaint, *result);
   return true;
 }
 
 static bool
+setInvalidateDuringPaint(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result)
+{
+  if (argCount != 1)
+    return false;
+
+  if (!NPVARIANT_IS_BOOLEAN(args[0]))
+    return false;
+  bool doInvalidate = NPVARIANT_TO_BOOLEAN(args[0]);
+
+  NPP npp = static_cast<TestNPObject*>(npobj)->npp;
+  InstanceData* id = static_cast<InstanceData*>(npp->pdata);
+  id->invalidateDuringPaint = doInvalidate;
+  return true;
+}
+
+static bool
 getError(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result)
 {
   if (argCount != 0)
     return false;
 
   NPP npp = static_cast<TestNPObject*>(npobj)->npp;
   InstanceData* id = static_cast<InstanceData*>(npp->pdata);
   if (id->err.str().length() == 0)
@@ -2333,16 +2353,25 @@ setColor(NPObject* npobj, const NPVarian
   VOID_TO_NPVARIANT(*result);
   return true;
 }
 
 void notifyDidPaint(InstanceData* instanceData)
 {
   ++instanceData->paintCount;
   instanceData->widthAtLastPaint = instanceData->window.width;
+
+  if (instanceData->invalidateDuringPaint) {
+    NPRect r;
+    r.left = 0;
+    r.top = 0;
+    r.right = instanceData->window.width;
+    r.bottom = instanceData->window.height;
+    NPN_InvalidateRect(instanceData->npp, &r);
+  }
 }
 
 static const NPClass kTestSharedNPClass = {
   NP_CLASS_STRUCT_VERSION,
   // Everything else is NULL
 };
 
 static bool getObjectValue(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result)

--- a/modules/plugin/test/testplugin/nptest.h
+++ b/modules/plugin/test/testplugin/nptest.h
@@ -97,16 +97,17 @@ typedef struct InstanceData {
   int32_t instanceCountWatchGeneration;
   bool lastReportedPrivateModeState;
   bool hasWidget;
   bool npnNewStream;
   bool throwOnNextInvoke;
   uint32_t timerID[2];
   bool timerTestResult;
   bool asyncCallbackResult;
+  bool invalidateDuringPaint;
   int32_t winX;
   int32_t winY;
   int32_t lastMouseX;
   int32_t lastMouseY;
   int32_t widthAtLastPaint;
   int32_t paintCount;
   int32_t writeCount;
   int32_t writeReadyCount;