Update WebrtcFrameScheduler to avoid concurrent captures.

remoting/protocol/webrtc_frame_scheduler_simple.cc

Index: remoting/protocol/webrtc_frame_scheduler_simple.cc
diff --git a/remoting/protocol/webrtc_frame_scheduler_simple.cc b/remoting/protocol/webrtc_frame_scheduler_simple.cc
index 336276d6609e20169c69af3b4aa86f95ad614a83..6b1c706392b3d7b5a50b24fefba53ee139204045 100644
--- a/remoting/protocol/webrtc_frame_scheduler_simple.cc
+++ b/remoting/protocol/webrtc_frame_scheduler_simple.cc
@@ -64,8 +64,7 @@ WebrtcFrameSchedulerSimple::~WebrtcFrameSchedulerSimple() {}
 void WebrtcFrameSchedulerSimple::OnKeyFrameRequested() {
   DCHECK(thread_checker_.CalledOnValidThread());
   key_frame_request_ = true;
-  if (!capture_timer_.IsRunning())
-    ScheduleNextFrame(base::TimeTicks::Now());
+  ScheduleNextFrame(base::TimeTicks::Now());
 }
 
 void WebrtcFrameSchedulerSimple::OnChannelParameters(int packet_loss,
@@ -109,6 +108,7 @@ bool WebrtcFrameSchedulerSimple::GetEncoderFrameParams(
 
   if (frame.updated_region().is_empty() && !top_off_is_active_ &&
       !key_frame_request_) {
+    frame_pending_ = false;
     ScheduleNextFrame(now);
     return false;
   }
@@ -157,6 +157,8 @@ void WebrtcFrameSchedulerSimple::OnFrameEncoded(
     const WebrtcVideoEncoder::EncodedFrame& encoded_frame,
     const webrtc::EncodedImageCallback::Result& send_result) {
   DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(frame_pending_);
+  frame_pending_ = false;
 
   base::TimeTicks now = base::TimeTicks::Now();
   pacing_bucket_.RefillOrSpill(encoded_frame.data.size(), now);
@@ -179,8 +181,10 @@ void WebrtcFrameSchedulerSimple::ScheduleNextFrame(base::TimeTicks now) {
 
   // Don't capture frames when paused or target bitrate is 0 or there is
   // no capture callback set.

[Jamie, 2016/10/18 22:40:26]

Update this comment. As written now, it's just an English transition of the
conditional, which doesn't seem very useful. You could just remove it, or
rephrase it in terms of why frames should not be scheduled under these
circumstances.

[Sergey Ulanov, 2016/10/18 23:11:02]

Removed it.

-  if (paused_ || pacing_bucket_.rate() == 0 || capture_callback_.is_null())
+  if (paused_ || pacing_bucket_.rate() == 0 || capture_callback_.is_null() ||
+      frame_pending_) {
     return;
+  }
 
   // If this is not the first frame then capture next frame after the previous
   // one has finished sending.
@@ -205,8 +209,9 @@ void WebrtcFrameSchedulerSimple::ScheduleNextFrame(base::TimeTicks now) {
 
 void WebrtcFrameSchedulerSimple::CaptureNextFrame() {
   DCHECK(thread_checker_.CalledOnValidThread());
-
+  DCHECK(!frame_pending_);
   last_capture_started_time_ = base::TimeTicks::Now();
+  frame_pending_ = true;
   capture_callback_.Run();
 }