Fix Omnibox.CharTypedToRepaintLatency regression with D3DVsync experiment

cc/scheduler/begin_frame_source.cc

 // Copyright 2014 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.
 
 #include "cc/scheduler/begin_frame_source.h"
 
 #include <stddef.h>
 
 #include "base/atomic_sequence_num.h"
 #include "base/auto_reset.h"
@@ skipping 266 matching lines @@
   DCHECK(obs);
   DCHECK(observers_.find(obs) == observers_.end());
 
   bool observers_was_empty = observers_.empty();
   observers_.insert(obs);
   obs->OnBeginFrameSourcePausedChanged(paused_);
   if (observers_was_empty)
     client_->OnNeedsBeginFrames(true);
 
   // Send a MISSED begin frame if necessary.
-  if (last_begin_frame_args_.IsValid()) {
-    const BeginFrameArgs& last_args = obs->LastUsedBeginFrameArgs();
-    if (!last_args.IsValid() ||
-        (last_begin_frame_args_.frame_time > last_args.frame_time)) {
-      DCHECK(
-          (last_begin_frame_args_.source_id != last_args.source_id) ||
-          (last_begin_frame_args_.sequence_number > last_args.sequence_number))
-          << "current " << last_begin_frame_args_.AsValue()->ToString()
-          << ", last " << last_args.AsValue()->ToString();
-      BeginFrameArgs missed_args = last_begin_frame_args_;
-      missed_args.type = BeginFrameArgs::MISSED;
-      obs->OnBeginFrame(missed_args);
-    }
-  }
+  BeginFrameArgs missed_args;
+  if (GetMissedBeginFrameArgs(obs, &missed_args))

[sunnyps, 2017/05/30 22:13:16]

nit: Can you add a DCHECK_EQ(missed_args.type, BeginFrameArgs::MISSED) here?

[stanisc, 2017/05/31 01:17:52]

Done.

+    obs->OnBeginFrame(missed_args);
 }
 
 void ExternalBeginFrameSource::RemoveObserver(BeginFrameObserver* obs) {
   DCHECK(obs);
   DCHECK(observers_.find(obs) != observers_.end());
 
   observers_.erase(obs);
   if (observers_.empty()) {
     last_begin_frame_args_ = BeginFrameArgs();

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

nit: Can you remove this line: last_begin_frame_args_ = BeginFrameArgs() ?

This variable used to be called missed_begin_frame_args_ but I changed it a
while back to actually be the same as last_begin_frame_args_. I should've
removed this line. This is the reason for the special workaround in
GpuVsyncBFS::GetMissedBeginFrameArgs.

[stanisc, 2017/05/31 01:17:52]

Done.

     client_->OnNeedsBeginFrames(false);
   }
 }
 
 void ExternalBeginFrameSource::DidFinishFrame(BeginFrameObserver* obs,
                                               const BeginFrameAck& ack) {}
 
 bool ExternalBeginFrameSource::IsThrottled() const {
   return true;
 }
@@ skipping 18 matching lines @@
     if (!last_args.IsValid() || (args.frame_time > last_args.frame_time)) {
       DCHECK((args.source_id != last_args.source_id) ||
              (args.sequence_number > last_args.sequence_number))
           << "current " << args.AsValue()->ToString() << ", last "
           << last_args.AsValue()->ToString();
       obs->OnBeginFrame(args);
     }
   }
 }
 
+bool ExternalBeginFrameSource::GetMissedBeginFrameArgs(
+    BeginFrameObserver* obs,
+    BeginFrameArgs* missed_args) {
+  if (!last_begin_frame_args_.IsValid())
+    return false;
+
+  const BeginFrameArgs& last_args = obs->LastUsedBeginFrameArgs();
+  if (last_args.IsValid() &&
+      last_begin_frame_args_.frame_time == last_args.frame_time) {
+    return false;
+  }
+
+  DCHECK((last_begin_frame_args_.source_id != last_args.source_id) ||
+         (last_begin_frame_args_.sequence_number > last_args.sequence_number))
+      << "current " << last_begin_frame_args_.AsValue()->ToString() << ", last "
+      << last_args.AsValue()->ToString();
+  *missed_args = last_begin_frame_args_;
+  missed_args->type = BeginFrameArgs::MISSED;
+  return true;
+}
+
 }  // namespace cc