Add Set Authoritative VSync Interval function

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 143c3ff54489573b1e22bf3a2a35ee17fecb1d95..95e91b9c198b888e104f327f878002c9c747a566 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),
@@ -166,9 +167,12 @@ 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())
+  if (authoritative_vsync_interval_ != base::TimeDelta()) {
+    interval = authoritative_vsync_interval_;
+  } else if (interval == base::TimeDelta()) {
+    // TODO(brianderson): We should not be receiving 0 intervals.
     interval = BeginFrameArgs::DefaultInterval();
+  }
 
   if (vsync_observer_)
     vsync_observer_->OnUpdateVSyncParameters(timebase, interval);
@@ -449,6 +453,10 @@ void Scheduler::SetChildrenNeedBeginFrames(bool children_need_begin_frames) {
   DCHECK_EQ(state_machine_.NextAction(), SchedulerStateMachine::ACTION_NONE);
 }
 
+void Scheduler::SetAuthoritativeVSyncInterval(base::TimeDelta interval) {

[simonhong, 2014/12/11 23:09:46]

nit: How about add DCHECK(settings_.forward_begin_frame_source); ?

SetAuthoritativeVSyncInterval() will only be called on that mode.

+  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() {