cc: Track BeginMainFrame more precisely in CompositorTimingHistory.

cc/scheduler/scheduler.h

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_SCHEDULER_SCHEDULER_H_
 #define CC_SCHEDULER_SCHEDULER_H_
 
 #include <deque>
 #include <string>
 
@@ skipping 107 matching lines @@
   bool PrepareTilesPending() const {
     return state_machine_.PrepareTilesPending();
   }
   bool BeginImplFrameDeadlinePending() const {
     return !begin_impl_frame_deadline_task_.IsCancelled();
   }
   bool ImplLatencyTakesPriority() const {
     return state_machine_.impl_latency_takes_priority();
   }
 
-  void NotifyBeginMainFrameStarted();
+  // Pass in a main_thread_start_time of base::TimeTicks() if it is not
+  // known (e.g. blink lives on a remote machine) to signal that the
+  // start time isn't known and should not be used for scheduling
+  // and statistics puposes.

[Sami, 2015/11/05 14:42:36]

nit: I'm not sure if the remote machine example is more mystifying or helpful :)
Would the single thread proxy case be better?

[brianderson, 2015/11/05 21:33:26]

With STP, we can still get valid timestamps. I checked with dtrainor and he said
I could change this to "(e.g. blink is running on a remote channel)" which
aligns more with where the code for "channel_main.h" is heading.

[Sami, 2015/11/06 11:27:49]

Ah right, looks like I misread STP as passing in a zero timeticks but that's
actually not the case. Speaking about channels sgtm.

+  void NotifyBeginMainFrameStarted(base::TimeTicks main_thread_start_time);
 
   base::TimeTicks LastBeginImplFrameTime();
 
   void SetDeferCommits(bool defer_commits);
 
   scoped_refptr<base::trace_event::ConvertableToTraceFormat> AsValue() const;
   void AsValueInto(base::trace_event::TracedValue* value) const override;
 
   void SetChildrenNeedBeginFrames(bool children_need_begin_frames);
   void SetVideoNeedsBeginFrames(bool video_needs_begin_frames);
@@ skipping 27 matching lines @@
   base::TimeDelta authoritative_vsync_interval_;
   base::TimeTicks last_vsync_timebase_;
 
   scoped_ptr<CompositorTimingHistory> compositor_timing_history_;
   base::TimeDelta estimated_parent_draw_time_;
 
   std::deque<BeginFrameArgs> begin_retro_frame_args_;
   SchedulerStateMachine::BeginImplFrameDeadlineMode
       begin_impl_frame_deadline_mode_;
   BeginFrameTracker begin_impl_frame_tracker_;
+  BeginFrameArgs begin_main_frame_args_;
 
   base::Closure begin_retro_frame_closure_;
   base::Closure begin_impl_frame_deadline_closure_;
   base::CancelableClosure begin_retro_frame_task_;
   base::CancelableClosure begin_impl_frame_deadline_task_;
 
   SchedulerStateMachine state_machine_;
   bool inside_process_scheduled_actions_;
   SchedulerStateMachine::Action inside_action_;
 
@@ skipping 36 matching lines @@
   }
 
   base::WeakPtrFactory<Scheduler> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Scheduler);
 };
 
 }  // namespace cc
 
 #endif  // CC_SCHEDULER_SCHEDULER_H_