cc: Add SwapAck watchdog.

cc/scheduler/compositor_timing_history.h

Index: cc/scheduler/compositor_timing_history.h
diff --git a/cc/scheduler/compositor_timing_history.h b/cc/scheduler/compositor_timing_history.h
index 0366a053f86237413ec9063aa051c73af0b62cdb..04b52fc5bb926de3a73254eb4333393e7ee561d7 100644
--- a/cc/scheduler/compositor_timing_history.h
+++ b/cc/scheduler/compositor_timing_history.h
@@ -31,6 +31,7 @@ class CC_EXPORT CompositorTimingHistory {
 
   CompositorTimingHistory(
       bool using_synchronous_renderer_compositor,
+      bool enable_swap_ack_watchdog,
       UMACategory uma_category,
       RenderingStatsInstrumentation* rendering_stats_instrumentation);
   virtual ~CompositorTimingHistory();
@@ -117,6 +118,10 @@ class CC_EXPORT CompositorTimingHistory {
   base::TimeTicks draw_start_time_;
   base::TimeTicks swap_start_time_;
 
+  // Watchdog timers.
+  bool swap_ack_watchdog_enabled_;
+  int swap_ack_watchdog_begin_impl_frame_count_;
+
   std::unique_ptr<UMAReporter> uma_reporter_;
   RenderingStatsInstrumentation* rendering_stats_instrumentation_;