Oilpan: move 2D Canvas and WebGL objects to the heap.

Source/platform/heap/Handle.h

Index: Source/platform/heap/Handle.h
diff --git a/Source/platform/heap/Handle.h b/Source/platform/heap/Handle.h
index 918a73135e39b7dbef858ae868b5a00a404fe9a0..2ed21661f17d2269c56f64b6adc1d69f35509e28 100644
--- a/Source/platform/heap/Handle.h
+++ b/Source/platform/heap/Handle.h
@@ -676,22 +676,29 @@ public:
     }
 };
 
-template<bool needsTracing, typename T>
-struct StdPairHelper;
+template<typename T, bool needsTracing>
+struct TraceIfEnabled;
 
 template<typename T>
-struct StdPairHelper<false, T>  {
+struct TraceIfEnabled<T, false>  {
     static void trace(Visitor*, T*) { }
 };
 
 template<typename T>
-struct StdPairHelper<true, T> {
+struct TraceIfEnabled<T, true> {
     static void trace(Visitor* visitor, T* t)
     {
         visitor->trace(*t);
     }
 };
 
+template <typename T> struct RemoveHeapPointerWrapperTypes {
+    typedef typename WTF::RemoveTemplate<typename WTF::RemoveTemplate<typename WTF::RemoveTemplate<T, Member>::Type, WeakMember>::Type, RawPtr>::Type Type;
+};
+
+template<typename T>
+struct TraceIfNeeded : public TraceIfEnabled<T, WebCore::IsGarbageCollectedType<typename RemoveHeapPointerWrapperTypes<typename WTF::RemovePointer<T>::Type>::Type>::value> { };

[zerny-chromium, 2014/08/01 08:05:15]

I don't think this trait does what we would like it to do. It is used in
Nullable (and ScriptPromiseProperty) to trace a (nullable) value object. So
first of all it is more lax in that it is also defined for non-values (ie, all
GC derived types) when it is only used for part-object allocated collections.
More importantly it is too narrow since it will not identify that a value object
with a trace method should be traced (ie, any object using DISALLOW_ALLOCATION
but with traced fields).

In short, I think we should use the existing NeedsTracing trait here. It is
default defined to be true if the type has a trace method and specialized for
the various other types (eg, Member) already. I'll upload a CL shortly.

+
 // This trace trait for std::pair will null weak members if their referent is
 // collected. If you have a collection that contain weakness it does not remove
 // entries from the collection that contain nulled weak members.
@@ -702,8 +709,8 @@ public:
     static const bool secondNeedsTracing = WTF::NeedsTracing<U>::value || WTF::IsWeak<U>::value;
     static void trace(Visitor* visitor, std::pair<T, U>* pair)
     {
-        StdPairHelper<firstNeedsTracing, T>::trace(visitor, &pair->first);
-        StdPairHelper<secondNeedsTracing, U>::trace(visitor, &pair->second);
+        TraceIfEnabled<T, firstNeedsTracing>::trace(visitor, &pair->first);
+        TraceIfEnabled<U, secondNeedsTracing>::trace(visitor, &pair->second);
     }
 };