[cc] Adds source_id and sequence_number to BeginFrameArgs.

ui/android/window_android.cc

Index: ui/android/window_android.cc
diff --git a/ui/android/window_android.cc b/ui/android/window_android.cc
index 79472befe6973cb2f905d9ef992650f92122fd6a..69c6f5c25fbfa5bf4cc9b33ab5372cc4892b86c7 100644
--- a/ui/android/window_android.cc
+++ b/ui/android/window_android.cc
@@ -30,6 +30,7 @@ class WindowAndroid::WindowBeginFrameSource : public cc::BeginFrameSource {
   explicit WindowBeginFrameSource(WindowAndroid* window)
       : window_(window),
         observer_count_(0),
+        next_sequence_number_(cc::BeginFrameArgs::kStartingFrameNumber),
         in_on_vsync_(false) {}
   ~WindowBeginFrameSource() override {}
 
@@ -40,14 +41,14 @@ class WindowAndroid::WindowBeginFrameSource : public cc::BeginFrameSource {
                       size_t remaining_frames) override {}
   bool IsThrottled() const override { return true; }
 
-  void OnVSync(base::TimeTicks frame_time,
-               base::TimeDelta vsync_period);
+  void OnVSync(base::TimeTicks frame_time, base::TimeDelta vsync_period);
 
  private:
   WindowAndroid* const window_;
   base::ObserverList<cc::BeginFrameObserver> observers_;
   int observer_count_;
   cc::BeginFrameArgs last_begin_frame_args_;
+  uint64_t next_sequence_number_;
   bool in_on_vsync_;
 };
 
@@ -67,6 +68,8 @@ void WindowAndroid::WindowBeginFrameSource::AddObserver(
     cc::BeginFrameArgs last_args = obs->LastUsedBeginFrameArgs();
     if (!last_args.IsValid() ||
         last_args.frame_time < last_begin_frame_args_.frame_time) {
+      DCHECK(last_args.sequence_number <

[brianderson, 2016/12/16 17:53:38]

Is it possible for the source id to change?
If yes: Does this DCHECK need to be guarded by a source id check?
If no: Please add a DCHECK that the source_id does not change.

[Eric Seckler, 2016/12/20 12:52:29]

I think you're right, the observer could switch windows, thus last_args may have
a different source_id. Adding the source_id check.

+             last_begin_frame_args_.sequence_number);
       last_begin_frame_args_.type = cc::BeginFrameArgs::MISSED;
       // TODO(crbug.com/602485): A deadline doesn't make too much sense
       // for a missed BeginFrame (the intention rather is 'immediately'),
@@ -95,9 +98,9 @@ void WindowAndroid::WindowBeginFrameSource::OnVSync(
     base::TimeDelta vsync_period) {
   // frame time is in the past, so give the next vsync period as the deadline.
   base::TimeTicks deadline = frame_time + vsync_period;
-  last_begin_frame_args_ =
-      cc::BeginFrameArgs::Create(BEGINFRAME_FROM_HERE, frame_time, deadline,
-                                 vsync_period, cc::BeginFrameArgs::NORMAL);
+  last_begin_frame_args_ = cc::BeginFrameArgs::Create(
+      BEGINFRAME_FROM_HERE, source_id(), next_sequence_number_++, frame_time,
+      deadline, vsync_period, cc::BeginFrameArgs::NORMAL);
   DCHECK(last_begin_frame_args_.IsValid());
 
   // We support adding/removing observers during observer iteration through