cc: Add main frame timing info to frame timing tracker.

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index ed8c0a2d3487a471180ced8a5809fc94a5f4fea8..8908d0d831497b73bab7ab8d016acc204c8292b0 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -324,10 +324,14 @@ base::TimeTicks Scheduler::AnticipatedDrawTime() const {
   return timebase + (begin_impl_frame_args_.interval * intervals);
 }
 
-base::TimeTicks Scheduler::LastBeginImplFrameTime() {
+base::TimeTicks Scheduler::LastBeginImplFrameTime() const {
   return begin_impl_frame_args_.frame_time;
 }
 
+base::TimeTicks Scheduler::NextBeginImplFrameTimeIfRequested() const {
+  return begin_impl_frame_args_.frame_time + begin_impl_frame_args_.interval;
+}
+
 void Scheduler::SetupNextBeginFrameIfNeeded() {
   if (!task_runner_.get())
     return;