Addressed haraken's feedback on the removal of WebGLObject maps.

third_party/WebKit/Source/modules/webgl/WebGLContextGroup.cpp

 /*
  * 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 29 matching lines @@
     return nullptr;
 
   // Weak processing removes dead entries from the HeapHashSet, so it's
   // guaranteed that this will not return null for the reason that a
   // WeakMember was nulled out.
   return (*m_contexts.begin())->contextGL();
 }
 
 void WebGLContextGroup::addContext(WebGLRenderingContextBase* context) {
   m_contexts.add(context);
+  ScriptWrappableVisitor::writeBarrier(this, context);
 }
 
 void WebGLContextGroup::loseContextGroup(
     WebGLRenderingContextBase::LostContextMode mode,
     WebGLRenderingContextBase::AutoRecoveryMethod autoRecoveryMethod) {
   ++m_numberOfContextLosses;
   for (WebGLRenderingContextBase* const context : m_contexts)
     context->loseContextImpl(mode, autoRecoveryMethod);
 }
 
 uint32_t WebGLContextGroup::numberOfContextLosses() const {
   return m_numberOfContextLosses;
 }
 
 DEFINE_TRACE_WRAPPERS(WebGLContextGroup) {
   // TODO(kbr, mlippautz): need to use the manual write barrier since we
   // need to use weak members to get the desired semantics in Oilpan, but
   // no such TraceWrapperMember (like TraceWrapperWeakMember) exists yet.
   for (auto context : m_contexts) {
     visitor->traceWrappersWithManualWriteBarrier(context);
   }
 }
 
 }  // namespace blink