Change LayerHostImpl to use frame time from BeginFrameArgs rather than ::Now()

cc/test/fake_layer_tree_host_impl.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_H_
 #define CC_TEST_FAKE_LAYER_TREE_HOST_IMPL_H_
 
 #include "cc/test/fake_layer_tree_host_impl_client.h"
 #include "cc/test/fake_rendering_stats_instrumentation.h"
 #include "cc/trees/layer_tree_host_impl.h"
 #include "cc/trees/single_thread_proxy.h"
 
 namespace cc {
 
 class FakeLayerTreeHostImpl : public LayerTreeHostImpl {
  public:
   explicit FakeLayerTreeHostImpl(Proxy* proxy);
   FakeLayerTreeHostImpl(const LayerTreeSettings& settings, Proxy* proxy);
   virtual ~FakeLayerTreeHostImpl();
 
   void ForcePrepareToDraw() {
     LayerTreeHostImpl::FrameData frame_data;
     PrepareToDraw(&frame_data, gfx::Rect());
     DidDrawAllLayers(frame_data);
   }
 
   virtual void CreatePendingTree() OVERRIDE;
 
-  virtual base::TimeTicks CurrentFrameTimeTicks() OVERRIDE;
+  virtual base::TimeTicks CurrentFrameTimeTicks() const OVERRIDE;
   void SetCurrentFrameTimeTicks(base::TimeTicks current_frame_time_ticks);
 
   using LayerTreeHostImpl::ActivatePendingTree;
   using LayerTreeHostImpl::manage_tiles_needed;
 
  private:
   base::TimeTicks current_frame_time_ticks_;
   FakeLayerTreeHostImplClient client_;
   FakeRenderingStatsInstrumentation stats_instrumentation_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_FAKE_LAYER_TREE_HOST_IMPL_H_