Fix DelegatedFrameResourceCollection thread safety

cc/layers/delegated_frame_resource_collection.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/delegated_frame_resource_collection.h"
 
 #include "base/bind.h"
 #include "cc/trees/blocking_task_runner.h"
 
 namespace cc {
 
 DelegatedFrameResourceCollection::DelegatedFrameResourceCollection()
     : client_(NULL),
       main_thread_runner_(BlockingTaskRunner::current()),
-      lost_all_resources_(false) {
+      lost_all_resources_(false),
+      weak_ptr_factory_(this) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
 }
 
 DelegatedFrameResourceCollection::~DelegatedFrameResourceCollection() {
   DCHECK(main_thread_checker_.CalledOnValidThread());
 }
 
 void DelegatedFrameResourceCollection::SetClient(
     DelegatedFrameResourceCollectionClient* client) {
   client_ = client;
@@ skipping 79 matching lines @@
     client_->UnusedResourcesAreAvailable();
 }
 
 void DelegatedFrameResourceCollection::RefResources(
     const TransferableResourceArray& resources) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   for (size_t i = 0; i < resources.size(); ++i)
     resource_id_ref_count_map_[resources[i].id].refs_to_wait_for++;
 }
 
-ReturnCallback
-DelegatedFrameResourceCollection::GetReturnResourcesCallbackForImplThread() {
-  return base::Bind(
-      &DelegatedFrameResourceCollection::UnrefResourcesOnImplThread,
-      this,
-      main_thread_runner_);
-}
-
-void DelegatedFrameResourceCollection::UnrefResourcesOnImplThread(
+static void UnrefResourcesOnImplThread(
+    base::WeakPtr<DelegatedFrameResourceCollection> self,
     scoped_refptr<BlockingTaskRunner> main_thread_runner,
     const ReturnedResourceArray& returned) {
   main_thread_runner->PostTask(
       FROM_HERE,
       base::Bind(
-          &DelegatedFrameResourceCollection::UnrefResources, this, returned));
+          &DelegatedFrameResourceCollection::UnrefResources, self, returned));
+}
+
+ReturnCallback
+DelegatedFrameResourceCollection::GetReturnResourcesCallbackForImplThread() {
+  return base::Bind(&UnrefResourcesOnImplThread,
+                    weak_ptr_factory_.GetWeakPtr(),
+                    main_thread_runner_);
 }
 
 }  // namespace cc