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 ba1af7328153c30fe9b571736f0cad981d9b00e9..90c32d1b0db82d9732fe54531d3d03e925c0d4c9 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -325,10 +325,14 @@ 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;