Fix DelegatedFrameResourceCollection thread safety

cc/layers/delegated_frame_resource_collection.h

 // 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.
 
 #ifndef CC_LAYERS_DELEGATED_FRAME_RESOURCE_COLLECTION_H_
 #define CC_LAYERS_DELEGATED_FRAME_RESOURCE_COLLECTION_H_
 
 #include "base/containers/hash_tables.h"
 #include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
 #include "base/threading/thread_checker.h"
 #include "cc/base/cc_export.h"
 #include "cc/resources/return_callback.h"
 #include "cc/resources/returned_resource.h"
 #include "cc/resources/transferable_resource.h"
 
 namespace cc {
 class BlockingTaskRunner;
 
 class CC_EXPORT DelegatedFrameResourceCollectionClient {
@@ skipping 19 matching lines @@
   // Methods for DelegatedFrameProvider.
   void RefResources(const TransferableResourceArray& resources);
   void UnrefResources(const ReturnedResourceArray& returned);
   void ReceivedResources(const TransferableResourceArray& resources);
   ReturnCallback GetReturnResourcesCallbackForImplThread();
 
  private:
   friend class base::RefCounted<DelegatedFrameResourceCollection>;
   ~DelegatedFrameResourceCollection();
 
-  void UnrefResourcesOnImplThread(
-      scoped_refptr<BlockingTaskRunner> main_thread_runner,
-      const ReturnedResourceArray& returned);
-
   DelegatedFrameResourceCollectionClient* client_;
   scoped_refptr<BlockingTaskRunner> main_thread_runner_;
 
   ReturnedResourceArray returned_resources_for_child_compositor_;
   bool lost_all_resources_;
 
   struct RefCount {
     int refs_to_return;
     int refs_to_wait_for;
   };
   typedef base::hash_map<unsigned, RefCount> ResourceIdRefCountMap;
   ResourceIdRefCountMap resource_id_ref_count_map_;
 
   base::ThreadChecker main_thread_checker_;
+  base::WeakPtrFactory<DelegatedFrameResourceCollection> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DelegatedFrameResourceCollection);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_DELEGATED_FRAME_RESOURCE_COLLECTION_H_