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

cc/test/fake_layer_tree_host_impl.cc

 // 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.
 
 #include "cc/test/fake_layer_tree_host_impl.h"
 #include "cc/trees/layer_tree_impl.h"
 
 namespace cc {
 
 FakeLayerTreeHostImpl::FakeLayerTreeHostImpl(Proxy* proxy)
@@ skipping 22 matching lines @@
 
 FakeLayerTreeHostImpl::~FakeLayerTreeHostImpl() {}
 
 void FakeLayerTreeHostImpl::CreatePendingTree() {
   LayerTreeHostImpl::CreatePendingTree();
   float arbitrary_large_page_scale = 100000.f;
   pending_tree()->SetPageScaleFactorAndLimits(
       1.f, 1.f / arbitrary_large_page_scale, arbitrary_large_page_scale);
 }
 
-base::TimeTicks FakeLayerTreeHostImpl::CurrentFrameTimeTicks() {
+base::TimeTicks FakeLayerTreeHostImpl::CurrentFrameTimeTicks() const {
   if (current_frame_time_ticks_.is_null())
     return LayerTreeHostImpl::CurrentFrameTimeTicks();
   return current_frame_time_ticks_;
 }
 
 void FakeLayerTreeHostImpl::SetCurrentFrameTimeTicks(
     base::TimeTicks current_frame_time_ticks) {
   current_frame_time_ticks_ = current_frame_time_ticks;
 }
 
 }  // namespace cc