Use strong references from WebGLContextGroup to WebGLRenderingContextBase.

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() {
-  // 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.
+  DCHECK(!m_contexts.isEmpty());
   return (*m_contexts.begin())->contextGL();
 }
 
 void WebGLContextGroup::addContext(WebGLRenderingContextBase* context) {
-  m_contexts.add(context);
-  ScriptWrappableVisitor::writeBarrier(this, context);
+  m_contexts.add(TraceWrapperMember<WebGLRenderingContextBase>(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);
+    visitor->traceWrappers(context);
   }
 }
 
 }  // namespace blink