Use a new type of weak phantom handle for ScriptWrappable.

third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 297 matching lines @@
         gcPrologueForMajorGC(isolate, flags & v8::kGCCallbackFlagConstructRetainedObjectInfos);
         break;
     case v8::kGCTypeProcessWeakCallbacks:
         TRACE_EVENT_BEGIN2("devtools.timeline,v8", "MajorGC", "usedHeapSizeBefore", usedHeapSize(isolate), "type", "weak processing");
         break;
     default:
         ASSERT_NOT_REACHED();
     }
 }
 
+namespace {
+
+void UpdateCollectedPhantomHandles(v8::Isolate* isolate)
+{
+    ThreadHeapStats& heapStats = ThreadState::current()->heap().heapStats();
+    size_t count = isolate->NumberOfPhantomHandleResetsSinceLastCall();
+    heapStats.decreaseWrapperCount(count);

[dominicc (has gone to gerrit), 2016/05/11 03:38:30]

Does this mean that phantom handles should *only* be used for wrappers, once per
wrapper?

[haraken, 2016/05/11 03:48:38]

Not really. heapStats.decreaseWrapperCount is just used as a hint to trigger
Oilpan's GCs, so the counter doesn't need to be very accurate.
heapStats.decreaseWrapperCount counts the number of V8 things that will have
references to Oilpan's objects.

+    heapStats.increaseCollectedWrapperCount(count);
+}
+
+} // namespace
+
 void V8GCController::gcEpilogue(v8::Isolate* isolate, v8::GCType type, v8::GCCallbackFlags flags)
 {
+    UpdateCollectedPhantomHandles(isolate);
     switch (type) {
     case v8::kGCTypeScavenge:
         TRACE_EVENT_END1("devtools.timeline,v8", "MinorGC", "usedHeapSizeAfter", usedHeapSize(isolate));
         // TODO(haraken): Remove this. See the comment in gcPrologue.
         if (ThreadState::current())
             ThreadState::current()->scheduleV8FollowupGCIfNeeded(BlinkGC::V8MinorGC);
         break;
     case v8::kGCTypeMarkSweepCompact:
         TRACE_EVENT_END1("devtools.timeline,v8", "MajorGC", "usedHeapSizeAfter", usedHeapSize(isolate));
         if (ThreadState::current())
@@ skipping 154 matching lines @@
     DEFINE_THREAD_SAFE_STATIC_LOCAL(CustomCountHistogram, scanPendingActivityHistogram, new CustomCountHistogram("Blink.ScanPendingActivityDuration", 1, 1000, 50));
     double startTime = WTF::currentTimeMS();
     v8::HandleScope scope(isolate);
     PendingActivityVisitor visitor(isolate, executionContext);
     toIsolate(executionContext)->VisitHandlesWithClassIds(&visitor);
     scanPendingActivityHistogram.count(static_cast<int>(WTF::currentTimeMS() - startTime));
     return visitor.pendingActivityFound();
 }
 
 } // namespace blink