cc: Control defer_commits logic by Scheduler

cc/scheduler/scheduler_state_machine.cc

Index: cc/scheduler/scheduler_state_machine.cc
diff --git a/cc/scheduler/scheduler_state_machine.cc b/cc/scheduler/scheduler_state_machine.cc
index 94016f3d5eb297c62ec496543749905254c4eba9..2cb2311f6de364d544c059a81d73c62126390224 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -49,7 +49,8 @@ SchedulerStateMachine::SchedulerStateMachine(const SchedulerSettings& settings)
       skip_next_begin_main_frame_to_reduce_latency_(false),
       skip_begin_main_frame_to_reduce_latency_(false),
       continuous_painting_(false),
-      impl_latency_takes_priority_on_battery_(false) {
+      impl_latency_takes_priority_on_battery_(false),
+      defer_commits_(false) {
 }
 
 const char* SchedulerStateMachine::OutputSurfaceStateToString(
@@ -241,6 +242,7 @@ void SchedulerStateMachine::AsValueInto(base::debug::TracedValue* state,
   state->SetBoolean("continuous_painting", continuous_painting_);
   state->SetBoolean("impl_latency_takes_priority_on_battery",
                     impl_latency_takes_priority_on_battery_);
+  state->SetBoolean("defer_commits", defer_commits_);
   state->EndDictionary();
 }
 
@@ -442,6 +444,10 @@ bool SchedulerStateMachine::CouldSendBeginMainFrame() const {
   if (!visible_)
     return false;
 
+  // We do not need new commits if it is deferred.
+  if (defer_commits_)
+    return false;
+
   return true;
 }
 
@@ -754,6 +760,10 @@ bool SchedulerStateMachine::SupportsProactiveBeginFrame() const {
   return !settings_.using_synchronous_renderer_compositor;
 }
 
+void SchedulerStateMachine::SetDeferCommits(bool defer_commits) {
+  defer_commits_ = defer_commits;
+}
+
 // These are the cases where we definitely (or almost definitely) have a
 // new frame to animate and/or draw and can draw.
 bool SchedulerStateMachine::BeginFrameNeededToAnimateOrDraw() const {
@@ -762,6 +772,10 @@ bool SchedulerStateMachine::BeginFrameNeededToAnimateOrDraw() const {
   if (!HasInitializedOutputSurface())
     return false;
 
+  // New BeginFrame should not be triggered during the commit is deferred.
+  if (defer_commits_)

[danakj, 2014/11/19 16:31:33]

Why is the ShouldSendBeginMainFrame() change not enough? Doesn't that happen
before calling this always?

[brianderson, 2014/11/19 19:55:07]

Agree that this check isn't needed. Deferring commit should prevent us from
needing to animate or draw. Also, if for some reason we _did_ need to draw the
active tree but wanted to defer commits, we'll need BeginFrames to draw the
active tree.

[simonhong, 2014/11/26 15:52:53]

Yep, I think you're right.
Deferring commit should not prevent BeginFrame triggering.

+    return false;
+
   // The forced draw respects our normal draw scheduling, so we need to
   // request a BeginImplFrame for it.
   if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW)
@@ -790,6 +804,10 @@ bool SchedulerStateMachine::ProactiveBeginFrameWanted() const {
   if (!visible_)
     return false;
 
+  // New BeginFrame should not be triggered during the commit is deferred.

[danakj, 2014/11/19 16:31:33]

ditto?

[brianderson, 2014/11/19 19:55:07]

ditto.

[simonhong, 2014/11/26 15:52:53]

Done.

+  if (defer_commits_)
+    return false;
+
   // We should proactively request a BeginImplFrame if a commit is pending
   // because we will want to draw if the commit completes quickly.
   if (needs_commit_ || commit_state_ != COMMIT_STATE_IDLE)