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

Source/core/html/canvas/WebGLContextGroup.h

 /*
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 #ifndef WebGLContextGroup_h
 #define WebGLContextGroup_h
 
 #include "core/html/canvas/WebGLRenderingContextBase.h"
+#include "platform/heap/Handle.h"
 #include "wtf/HashSet.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
 
 namespace blink {
 class WebGraphicsContext3D;
 }
 
 namespace WebCore {
 
 class WebGLExtension;
 class WebGLSharedObject;
 class WebGLRenderingContextBase;
 
 typedef int ExceptionCode;
 
-class WebGLContextGroup FINAL : public RefCounted<WebGLContextGroup> {
+class WebGLContextGroup FINAL : public RefCountedWillBeGarbageCollected<WebGLContextGroup> {
+    DECLARE_EMPTY_DESTRUCTOR_WILL_BE_REMOVED(WebGLContextGroup);
 public:
-    static PassRefPtr<WebGLContextGroup> create();
-    ~WebGLContextGroup();
+    static PassRefPtrWillBeRawPtr<WebGLContextGroup> create();
 
     void addContext(WebGLRenderingContextBase*);
     void removeContext(WebGLRenderingContextBase*);
 
     void addObject(WebGLSharedObject*);
     void removeObject(WebGLSharedObject*);
 
     blink::WebGraphicsContext3D* getAWebGraphicsContext3D();
 
     void loseContextGroup(WebGLRenderingContextBase::LostContextMode);
 
+    void trace(Visitor*);
+    void clearWeakMembers(Visitor*);
+
   private:
     friend class WebGLObject;
 
     WebGLContextGroup();
 
     void detachAndRemoveAllObjects();
 
-    HashSet<WebGLRenderingContextBase*> m_contexts;
-    HashSet<WebGLSharedObject*> m_groupObjects;
+    WillBeHeapHashSet<RawPtrWillBeWeakMember<WebGLRenderingContextBase> > m_contexts;

[sof, 2014/07/01 13:54:11]

Refer to the rendering contexts weakly, so as to not keep them alive when/if the
context group is the only reference.

The weak collecion serves another purpose also: being able to catch when all the
rendering contexts are about to disappear. At that point we have to evict all
the group objects, which we also keep references to weakly. See the declaration
below and clearWeakMembers() method for how that is currently handled.

+    WillBeHeapHashSet<RawPtrWillBeWeakMember<WebGLSharedObject> > m_groupObjects;
+
+#if ENABLE(OILPAN)
+    // Oilpan: Weak context references are kept, so in order to handle
+    // the case where all contexts fall away and the group objects
+    // will have to be flushed, we save away a 3D context object during
+    // tracing. It will be used during the weak callback only and cleared
+    // then.
+    blink::WebGraphicsContext3D* m_savedContext;
+#endif
 };
 
 } // namespace WebCore
 
 #endif // WebGLContextGroup_h