cc: Consider Surface active if frame received recently

cc/surfaces/display_scheduler.h

 // Copyright 2015 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_SURFACES_DISPLAY_SCHEDULER_H_
 #define CC_SURFACES_DISPLAY_SCHEDULER_H_
 
 #include "base/cancelable_callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 36 matching lines @@
 
   // BeginFrameObserverBase implementation
   bool OnBeginFrameDerivedImpl(const BeginFrameArgs& args) override;
 
  protected:
   base::TimeTicks DesiredBeginFrameDeadlineTime();
   virtual void ScheduleBeginFrameDeadline();
   void AttemptDrawAndSwap();
   void OnBeginFrameDeadline();
   void DrawAndSwap();
+  void UpdateActiveSurfaces();
 
   DisplaySchedulerClient* client_;
   BeginFrameSource* begin_frame_source_;
   base::SingleThreadTaskRunner* task_runner_;
 
   BeginFrameArgs current_begin_frame_args_;
   base::Closure begin_frame_deadline_closure_;
   base::CancelableClosure begin_frame_deadline_task_;
   base::TimeTicks begin_frame_deadline_task_time_;
 
   bool output_surface_lost_;
   bool root_surface_resources_locked_;
 
   bool inside_begin_frame_deadline_interval_;
   bool needs_draw_;
-  bool expecting_root_surface_damage_because_of_resize_;
-  bool all_active_child_surfaces_ready_to_draw_;
+  bool child_surfaces_ready_to_draw_;
 
   int pending_swaps_;
   int max_pending_swaps_;
 
   SurfaceId root_surface_id_;
   bool root_surface_damaged_;
-  bool expect_damage_from_root_surface_;
+  bool root_surface_active_;
+  bool expecting_root_surface_damage_because_of_resize_;
 
+  // We currently use a heuristic that considers a child surface
+  // active if it has submitted a frame anytime within the last 3
+  // vsyncs.
+  static const int kNumFramesSurfaceIsActive = 3;
   std::set<SurfaceId> child_surface_ids_damaged_;
-  std::set<SurfaceId> child_surface_ids_damaged_prev_;
-  std::vector<SurfaceId> child_surface_ids_to_expect_damage_from_;
+  std::set<SurfaceId> active_child_surface_ids_[kNumFramesSurfaceIsActive];
+  int active_child_surface_ids_index_;
 
   base::WeakPtrFactory<DisplayScheduler> weak_ptr_factory_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DisplayScheduler);
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_DISPLAY_SCHEDULER_H_