cc: Implement unified BeginFrame on aura

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 0cce5dc9adc6ea8dd58bd70da3ee6b12645ba1f1..99bd280e1ba0b27edea35adc8f9e860f7b906645 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -85,6 +85,7 @@ Scheduler::Scheduler(
       primary_frame_source_internal_(external_begin_frame_source.Pass()),
       background_frame_source_internal_(),
       vsync_observer_(NULL),
+      authoritative_vsync_interval_(base::TimeDelta()),
       settings_(scheduler_settings),
       client_(client),
       layer_tree_host_id_(layer_tree_host_id),
@@ -166,12 +167,18 @@ void Scheduler::OnPowerStateChange(bool on_battery_power) {
 
 void Scheduler::CommitVSyncParameters(base::TimeTicks timebase,
                                       base::TimeDelta interval) {
-  // TODO(brianderson): We should not be receiving 0 intervals.
-  if (interval == base::TimeDelta())
-    interval = BeginFrameArgs::DefaultInterval();
+  base::TimeDelta vsync_interval;
+  if (authoritative_vsync_interval_ != base::TimeDelta()) {
+    vsync_interval = authoritative_vsync_interval_;
+  } else if (interval == base::TimeDelta()) {
+    // TODO(brianderson): We should not be receiving 0 intervals.
+    vsync_interval = BeginFrameArgs::DefaultInterval();
+  } else {
+    vsync_interval = interval;
+  }
 
   if (vsync_observer_)
-    vsync_observer_->OnUpdateVSyncParameters(timebase, interval);
+    vsync_observer_->OnUpdateVSyncParameters(timebase, vsync_interval);
 }
 
 void Scheduler::SetEstimatedParentDrawTime(base::TimeDelta draw_time) {
@@ -449,6 +456,10 @@ void Scheduler::SetChildrenNeedBeginFrames(bool children_need_begin_frames) {
   DCHECK_EQ(state_machine_.NextAction(), SchedulerStateMachine::ACTION_NONE);
 }
 
+void Scheduler::SetAuthoritativeVSyncInterval(base::TimeDelta interval) {
+  authoritative_vsync_interval_ = interval;
+}
+
 // BeginRetroFrame is called for BeginFrames that we've deferred because
 // the scheduler was in the middle of processing a previous BeginFrame.
 void Scheduler::BeginRetroFrame() {