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

[sof, 2014/07/20 05:04:16]

The representation of these object references from this RefCounted<> object is
what remains to be settled, I believe -- see
https://codereview.chromium.org/365653002/diff/120001/Source/core/html/canvas...

I could expand the comment some more on why heap-based alternatives are
problematic, but the current representation and handling is acceptable and safe
to me.

+    // 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;

[haraken, 2014/07/22 03:46:10]

Probably we discussed this before, but why can't we use
PersistentHeapHashSet<WeakMember<WebGLRenderingContextBase>> ?

[sof, 2014/07/22 06:15:21]

Doesn't the above comment referring to (one of) the previous thread shed some
light on this? It will leak, I think, and prevent correct
finalization/detachment of the WebGLSharedObjects from here.

(This object will be simplified a fair bit if the graphics context will be able
to release all underlying resources, btw.)

 };