Fix Omnibox.CharTypedToRepaintLatency regression with D3DVsync experiment

content/browser/compositor/gpu_vsync_begin_frame_source.cc

Index: content/browser/compositor/gpu_vsync_begin_frame_source.cc
diff --git a/content/browser/compositor/gpu_vsync_begin_frame_source.cc b/content/browser/compositor/gpu_vsync_begin_frame_source.cc
index 7e43be479adc6b1ff83bc7337b8cf60b29b15855..cc1e793c528776c1b2a544e16722afac0e826434 100644
--- a/content/browser/compositor/gpu_vsync_begin_frame_source.cc
+++ b/content/browser/compositor/gpu_vsync_begin_frame_source.cc
@@ -22,7 +22,7 @@ void GpuVSyncBeginFrameSource::OnVSync(base::TimeTicks timestamp,
   if (!needs_begin_frames_)
     return;
 
-  base::TimeTicks now = base::TimeTicks::Now();
+  base::TimeTicks now = Now();
   base::TimeTicks deadline = now.SnappedToNextTick(timestamp, interval);
 
   TRACE_EVENT1("cc", "GpuVSyncBeginFrameSource::OnVSync", "latency",
@@ -39,4 +39,48 @@ void GpuVSyncBeginFrameSource::OnNeedsBeginFrames(bool needs_begin_frames) {
   vsync_control_->SetNeedsVSync(needs_begin_frames);
 }
 
+base::TimeTicks GpuVSyncBeginFrameSource::Now() const {
+  return base::TimeTicks::Now();
+}
+
+bool GpuVSyncBeginFrameSource::GetMissedBeginFrameArgs(
+    cc::BeginFrameObserver* obs,
+    cc::BeginFrameArgs* missed_args) {
+  const cc::BeginFrameArgs& last_observer_args = obs->LastUsedBeginFrameArgs();
+  if (!last_begin_frame_args_.IsValid()) {
+    // This is the case when all observers were removed from this BFS.
+    if (!last_observer_args.IsValid())

[sunnyps, 2017/05/30 22:13:17]

nit: Remove this workaround after removing the "last_begin_frame_args_ =
BeginFrameArgs" line from ExternalBFS.

[stanisc, 2017/05/31 01:17:53]

Done.

+      return false;
+
+    last_begin_frame_args_ = last_observer_args;
+  }
+
+  base::TimeTicks now = Now();
+  base::TimeTicks estimated_next_timestamp = now.SnappedToNextTick(
+      last_begin_frame_args_.frame_time, last_begin_frame_args_.interval);
+  base::TimeTicks missed_timestamp =
+      estimated_next_timestamp - last_begin_frame_args_.interval;
+
+  if (missed_timestamp > last_begin_frame_args_.frame_time) {
+    // The projected missed timestamp is newer than the last known timestamp.
+    // In this case create BeginFrameArgs with a new sequence number.
+    next_sequence_number_++;
+    last_begin_frame_args_ = cc::BeginFrameArgs::Create(
+        BEGINFRAME_FROM_HERE, source_id(), next_sequence_number_,
+        missed_timestamp, estimated_next_timestamp,
+        last_begin_frame_args_.interval, cc::BeginFrameArgs::MISSED);
+  } else {
+    // The last known args object is up-to-date. Skip sending notification
+    // if the observer has already seen it.
+    if (last_observer_args.IsValid() &&
+        last_begin_frame_args_.frame_time <= last_observer_args.frame_time) {
+      return false;
+    }
+  }
+
+  *missed_args = last_begin_frame_args_;
+  missed_args->type = cc::BeginFrameArgs::MISSED;
+  return true;
+}
+
 }  // namespace content