cc: Don't attempt main thread synchronization if it is slow.

cc/scheduler/scheduler.h

Index: cc/scheduler/scheduler.h
diff --git a/cc/scheduler/scheduler.h b/cc/scheduler/scheduler.h
index 5773bc453d33ea3336449c724b1f1de3dae10491..d76e4d238ed151dd26d2575b43932e1bb47cd342 100644
--- a/cc/scheduler/scheduler.h
+++ b/cc/scheduler/scheduler.h
@@ -99,7 +99,8 @@ class CC_EXPORT Scheduler : public BeginFrameObserverBase {
   void DidSwapBuffers();
   void DidSwapBuffersComplete();
 
-  void SetImplLatencyTakesPriority(bool impl_latency_takes_priority);
+  void SetSmoothnessMode(bool smoothness_takes_priority,

[Sami, 2015/11/06 11:54:42]

nit: some of the (test) call sites might read a bit better if this was split
into two setters. The naming is also a little confusing now since
|smoothness_takes_priority| only sometimes makes impl take priority :)

How about something like this:

SetImplLatencyIsImportant(...)
SetBestEffortMainSynchronizationEnabled(scroll_affects_scroll_handler)  // Later
we'd likely add rAF and CSS animation bits here.

Not totally happy with the naming but WDYT of the general idea?

[brianderson, 2015/11/12 20:22:04]

That sounds good. I might call the second one SetScrollAffectsScrollHandler, and
change the name again in the follow up patches.

+                         bool scroll_affects_scroll_handler);
 
   void NotifyReadyToCommit();
   void BeginMainFrameAborted(CommitEarlyOutReason reason);
@@ -126,7 +127,7 @@ class CC_EXPORT Scheduler : public BeginFrameObserverBase {
     return !begin_impl_frame_deadline_task_.IsCancelled();
   }
   bool ImplLatencyTakesPriority() const {
-    return state_machine_.impl_latency_takes_priority();
+    return state_machine_.ImplLatencyTakesPriority();
   }
 
   // Pass in a main_thread_start_time of base::TimeTicks() if it is not
@@ -201,9 +202,13 @@ class CC_EXPORT Scheduler : public BeginFrameObserverBase {
   void DrawAndSwapForced();
   void ProcessScheduledActions();
   void UpdateCompositorTimingHistoryRecordingEnabled();
-  bool ShouldRecoverMainLatency(const BeginFrameArgs& args) const;
-  bool ShouldRecoverImplLatency(const BeginFrameArgs& args) const;
-  bool CanCommitAndActivateBeforeDeadline(const BeginFrameArgs& args) const;
+  bool ShouldRecoverMainLatency(const BeginFrameArgs& args,
+                                bool can_activate_before_deadline) const;
+  bool ShouldRecoverImplLatency(const BeginFrameArgs& args,
+                                bool can_activate_before_deadline) const;
+  bool CanCommitAndActivateBeforeDeadline(
+      const BeginFrameArgs& args,
+      base::TimeDelta bmf_to_activate_estimate) const;
   void AdvanceCommitStateIfPossible();
   bool IsBeginMainFrameSentOrStarted() const;
   void BeginRetroFrame();