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

cc/trees/single_thread_proxy.cc

Index: cc/trees/single_thread_proxy.cc
diff --git a/cc/trees/single_thread_proxy.cc b/cc/trees/single_thread_proxy.cc
index 6498f0e0996ce49b310eb9a1c7a5d83bcfbfe4df..dd6f7b4a50d3df75c7d22b720849e2ee39dbee82 100644
--- a/cc/trees/single_thread_proxy.cc
+++ b/cc/trees/single_thread_proxy.cc
@@ -494,6 +494,7 @@ void SingleThreadProxy::CompositeImmediately(base::TimeTicks frame_begin_time) {
     BeginFrameArgs begin_frame_args(BeginFrameArgs::Create(
         BEGINFRAME_FROM_HERE, frame_begin_time, base::TimeTicks(),
         BeginFrameArgs::DefaultInterval(), BeginFrameArgs::SYNCHRONOUS));
+    layer_tree_host_impl_->UpdateCurrentBeginFrameArgs(begin_frame_args);
     DoBeginMainFrame(begin_frame_args);
     DoCommit();
 
@@ -519,6 +520,8 @@ void SingleThreadProxy::CompositeImmediately(base::TimeTicks frame_begin_time) {
     // another draw will never be scheduled, so break remaining promises.
     layer_tree_host_impl_->active_tree()->BreakSwapPromises(
         SwapPromise::SWAP_FAILS);
+
+    layer_tree_host_impl_->ResetCurrentBeginFrameArgsForNextFrame();
   }
 }
 
@@ -593,7 +596,6 @@ DrawResult SingleThreadProxy::DoComposite(base::TimeTicks frame_begin_time,
 
     bool start_ready_animations = draw_frame;
     layer_tree_host_impl_->UpdateAnimationState(start_ready_animations);
-    layer_tree_host_impl_->ResetCurrentBeginFrameArgsForNextFrame();
 
     timing_history_.DidFinishDrawing();
   }