Add decode() functionality to image elements.

cc/test/fake_layer_tree_host_impl_client.h

 // Copyright 2012 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_TEST_FAKE_LAYER_TREE_HOST_IMPL_CLIENT_H_
 #define CC_TEST_FAKE_LAYER_TREE_HOST_IMPL_CLIENT_H_
 
 #include "cc/output/begin_frame_args.h"
 #include "cc/trees/layer_tree_host_impl.h"
 
@@ skipping 18 matching lines @@
   bool IsInsideDraw() override;
   void RenewTreePriority() override {}
   void PostDelayedAnimationTaskOnImplThread(const base::Closure& task,
                                             base::TimeDelta delay) override {}
   void DidActivateSyncTree() override {}
   void WillPrepareTiles() override {}
   void DidPrepareTiles() override {}
   void DidCompletePageScaleAnimationOnImplThread() override {}
   void OnDrawForCompositorFrameSink(bool resourceless_software_draw) override {}
   void NeedsImplSideInvalidation() override {}
+  void NotifyImageDecodeRequestFinished() override {}
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_FAKE_LAYER_TREE_HOST_IMPL_CLIENT_H_