Correct comment related to WebGLContextGroup's weak references.

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 12 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "modules/webgl/WebGLContextGroup.h"
 
 namespace blink {
 
 WebGLContextGroup::WebGLContextGroup() : m_numberOfContextLosses(0) {}
 
 gpu::gles2::GLES2Interface* WebGLContextGroup::getAGLInterface() {
-  // During an Oilpan GC where WebGL objects become unreachable at the same
-  // time the context does, the m_contexts set can be fully cleared out
-  // before WebGLObjects' destructors run. Since the calling code handles
-  // this gracefully, explicitly test for this possibility.
+  // It's possible that all of the WebGLRenderingContextBases (currently
+  // only one) referenced weakly by this WebGLContextGroup are GC'd before
+  // the (shared) WebGLObjects that it created. Since the calling code
+  // handles this gracefully, and since the graphical resources will have
+  // been implicitly reclaimed by the deletion of the context, explicitly
+  // test for this possibility.
   if (m_contexts.isEmpty())
     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) {
@@ skipping 15 matching lines @@
 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