Revert of [Oilpan] Migrate classes under module/webgl onto oilpan heap

Source/modules/webgl/WebGLContextGroup.h

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 53 matching lines @@
 
     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;
-    GC_PLUGIN_IGNORE("http://crbug.com/516610")
     HashSet<WebGLSharedObject*> m_groupObjects;
 };
 
 } // namespace blink
 
 #endif // WebGLContextGroup_h