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

Source/core/html/canvas/WebGLContextGroup.h

Index: Source/core/html/canvas/WebGLContextGroup.h
diff --git a/Source/core/html/canvas/WebGLContextGroup.h b/Source/core/html/canvas/WebGLContextGroup.h
index 077b5d2effe8bfac170b61794b6e3bd27a989037..81fa41d476582f49c6b32fb23e45821ab03a6ef8 100644
--- a/Source/core/html/canvas/WebGLContextGroup.h
+++ b/Source/core/html/canvas/WebGLContextGroup.h
@@ -58,13 +58,19 @@ public:
 
     void loseContextGroup(WebGLRenderingContextBase::LostContextMode);
 
-  private:
+private:
     friend class WebGLObject;
 
     WebGLContextGroup();
 
     void detachAndRemoveAllObjects();
 
+    // FIXME: Oilpan: this object is not on the heap, but keeps bare
+    // pointers to garbage collected objects in the two hash sets
+    // below. The objects are responsible for managing their
+    // registration with WebGLContextGroup, and vice versa, the
+    // WebGLContextGroup takes care of detaching the group objects if
+    // the set of WebGLRenderingContextBase contexts becomes empty.
     HashSet<WebGLRenderingContextBase*> m_contexts;
     HashSet<WebGLSharedObject*> m_groupObjects;
 };