viz: Snap sequence numbers in BeginFrameArgs based on vsync.

This brings GpuVSyncBeginFrameSource in-line with how BeginFrameArgs is
generated in other sources (e.g. ExternalBeginFrameSourceAndroid, and
DelayBasedBeginFrameSource).

BUG=none

Change-Id: Ib6f126c15092c0dc3be35a3ee6953ea1c2a21c48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2058034Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Auto-Submit: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742427}

components/viz/service/frame_sinks/gpu_vsync_begin_frame_source.cc

@@ -23,10 +23,9 @@ GpuVSyncBeginFrameSource::~GpuVSyncBeginFrameSource() = default;
 
 void GpuVSyncBeginFrameSource::OnGpuVSync(base::TimeTicks vsync_time,
                                           base::TimeDelta vsync_interval) {
-  ExternalBeginFrameSource::OnBeginFrame(BeginFrameArgs::Create(
-      BEGINFRAME_FROM_HERE, source_id(), next_begin_frame_sequence_number_++,
-      vsync_time, vsync_time + vsync_interval, vsync_interval,
-      BeginFrameArgs::NORMAL));
+  auto begin_frame_args = begin_frame_args_generator_.GenerateBeginFrameArgs(
+      source_id(), vsync_time, vsync_time + vsync_interval, vsync_interval);
+  ExternalBeginFrameSource::OnBeginFrame(begin_frame_args);
 }
 
 BeginFrameArgs GpuVSyncBeginFrameSource::GetMissedBeginFrameArgs(
@@ -46,9 +45,8 @@ BeginFrameArgs GpuVSyncBeginFrameSource::GetMissedBeginFrameArgs(
   // Don't create new args unless we've actually moved past the previous frame.
   if (!last_begin_frame_args_.IsValid() ||
       frame_time > last_begin_frame_args_.frame_time) {
-    last_begin_frame_args_ = BeginFrameArgs::Create(
-        BEGINFRAME_FROM_HERE, source_id(), next_begin_frame_sequence_number_++,
-        frame_time, frame_time + interval, interval, BeginFrameArgs::NORMAL);
+    last_begin_frame_args_ = begin_frame_args_generator_.GenerateBeginFrameArgs(
+        source_id(), frame_time, frame_time + interval, interval);
   }
 
   return ExternalBeginFrameSource::GetMissedBeginFrameArgs(obs);

components/viz/service/frame_sinks/gpu_vsync_begin_frame_source.h

@@ -34,7 +34,7 @@ class VIZ_SERVICE_EXPORT GpuVSyncBeginFrameSource
   void OnGpuVSync(base::TimeTicks vsync_time, base::TimeDelta vsync_interval);
 
   OutputSurface* const output_surface_;
-  uint64_t next_begin_frame_sequence_number_ = 1;
+  BeginFrameArgsGenerator begin_frame_args_generator_;
 
   DISALLOW_COPY_AND_ASSIGN(GpuVSyncBeginFrameSource);
 };