Fix Omnibox.CharTypedToRepaintLatency regression with D3DVsync experiment

cc/scheduler/begin_frame_source.cc

Index: cc/scheduler/begin_frame_source.cc
diff --git a/cc/scheduler/begin_frame_source.cc b/cc/scheduler/begin_frame_source.cc
index be6394e617a88882f5806432ef0d3de16927d2cc..14f81585f6c8e869e0b4b597bb4bed095a2d063f 100644
--- a/cc/scheduler/begin_frame_source.cc
+++ b/cc/scheduler/begin_frame_source.cc
@@ -284,19 +284,10 @@ void ExternalBeginFrameSource::AddObserver(BeginFrameObserver* obs) {
     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 = GetMissedBeginFrameArgs(obs);
+  if (missed_args.IsValid()) {
+    DCHECK_EQ(BeginFrameArgs::MISSED, missed_args.type);
+    obs->OnBeginFrame(missed_args);
   }
 }
 
@@ -305,10 +296,8 @@ void ExternalBeginFrameSource::RemoveObserver(BeginFrameObserver* obs) {
   DCHECK(observers_.find(obs) != observers_.end());
 
   observers_.erase(obs);
-  if (observers_.empty()) {
-    last_begin_frame_args_ = BeginFrameArgs();
+  if (observers_.empty())
     client_->OnNeedsBeginFrames(false);
-  }
 }
 
 void ExternalBeginFrameSource::DidFinishFrame(BeginFrameObserver* obs,
@@ -345,4 +334,24 @@ void ExternalBeginFrameSource::OnBeginFrame(const BeginFrameArgs& args) {
   }
 }
 
+BeginFrameArgs ExternalBeginFrameSource::GetMissedBeginFrameArgs(
+    BeginFrameObserver* obs) {
+  if (!last_begin_frame_args_.IsValid())
+    return BeginFrameArgs();
+
+  const BeginFrameArgs& last_args = obs->LastUsedBeginFrameArgs();
+  if (last_args.IsValid() &&
+      last_begin_frame_args_.frame_time == last_args.frame_time) {
+    return BeginFrameArgs();
+  }
+
+  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;
+  return missed_args;
+}
+
 }  // namespace cc