Use a new type of weak phantom handle for ScriptWrappable.

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

Index: third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp b/third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp
index 70a0efcae5fb2130c03c28d68a31aadf140f9c04..c4c2922bc95a1d1438a2f3fd0baee667fe35c65a 100644
--- a/third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp
@@ -315,8 +315,21 @@ void V8GCController::gcPrologue(v8::Isolate* isolate, v8::GCType type, v8::GCCal
     }
 }
 
+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));