cc: Adding BeginFrameTracker object and removing Now() from LTHI.

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/begin_frame_args_test.h"
 #include "cc/test/fake_layer_tree_host_impl.h"
 #include "cc/test/test_shared_bitmap_manager.h"
 #include "cc/trees/layer_tree_impl.h"
 
 namespace cc {
@@ skipping 43 matching lines @@
 FakeLayerTreeHostImpl::~FakeLayerTreeHostImpl() {}
 
 void FakeLayerTreeHostImpl::CreatePendingTree() {
   LayerTreeHostImpl::CreatePendingTree();
   float arbitrary_large_page_scale = 100000.f;
   pending_tree()->PushPageScaleFromMainThread(
       1.f, 1.f / arbitrary_large_page_scale, arbitrary_large_page_scale);
 }
 
 BeginFrameArgs FakeLayerTreeHostImpl::CurrentBeginFrameArgs() const {
-  if (!current_begin_frame_args_.IsValid())
-    return LayerTreeHostImpl::CurrentBeginFrameArgs();
-  return current_begin_frame_args_;
+  return current_begin_frame_tracker_.DangerousMethodCurrentOrLast();
 }
 
 void FakeLayerTreeHostImpl::SetCurrentBeginFrameArgs(
     const BeginFrameArgs& args) {
-  current_begin_frame_args_ = args;
+  if (!current_begin_frame_tracker_.DangerousMethodHasFinished()) {
+    current_begin_frame_tracker_.Finish();
+  }
+  current_begin_frame_tracker_.Start(args);
 }
 
 int FakeLayerTreeHostImpl::RecursiveUpdateNumChildren(LayerImpl* layer) {
   int num_children_that_draw_content = 0;
   for (size_t i = 0; i < layer->children().size(); ++i) {
     num_children_that_draw_content +=
         RecursiveUpdateNumChildren(layer->children()[i]);
   }
   if (layer->DrawsContent() && layer->HasDelegatedContent())
     num_children_that_draw_content += 1000;
   layer->SetNumDescendantsThatDrawContent(num_children_that_draw_content);
   return num_children_that_draw_content + (layer->DrawsContent() ? 1 : 0);
 }
 
 void FakeLayerTreeHostImpl::UpdateNumChildrenAndDrawPropertiesForActiveTree() {
   UpdateNumChildrenAndDrawProperties(active_tree());
 }
 
 void FakeLayerTreeHostImpl::UpdateNumChildrenAndDrawProperties(
     LayerTreeImpl* layerTree) {
   RecursiveUpdateNumChildren(layerTree->root_layer());
   bool update_lcd_text = false;
   layerTree->UpdateDrawProperties(update_lcd_text);
 }
 
 }  // namespace cc