Fix for issue 684766 Old/erroneous frame feedback during tab capture

content/browser/renderer_host/media/video_capture_controller.cc

Index: content/browser/renderer_host/media/video_capture_controller.cc
diff --git a/content/browser/renderer_host/media/video_capture_controller.cc b/content/browser/renderer_host/media/video_capture_controller.cc
index 9902d94dad4e4b80de214b7b342299a6720d697c..0a2ef8b39f236fa4e5f9f6f721458ce7a8d44326 100644
--- a/content/browser/renderer_host/media/video_capture_controller.cc
+++ b/content/browser/renderer_host/media/video_capture_controller.cc
@@ -145,6 +145,11 @@ bool VideoCaptureController::BufferState::HasZeroConsumerHoldCount() {
   return consumer_hold_count_ == 0;
 }
 
+void VideoCaptureController::BufferState::SetFrameFeedbackId(int id) {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+  frame_feedback_id_ = id;
+}
+
 void VideoCaptureController::BufferState::SetConsumerFeedbackObserver(
     media::VideoFrameConsumerFeedbackObserver* consumer_feedback_observer) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
@@ -377,15 +382,16 @@ void VideoCaptureController::OnIncomingCapturedVideoFrame(
   DCHECK_NE(buffer_id, media::VideoCaptureBufferPool::kInvalidId);
 
   // Insert if not exists.
-  const auto it =
+  const auto insert_result =
       buffer_id_to_state_map_
           .insert(std::make_pair(
               buffer_id, BufferState(buffer_id, buffer.frame_feedback_id(),
                                      consumer_feedback_observer_.get(),
-                                     frame_buffer_pool_.get())))
-          .first;
-  BufferState& buffer_state = it->second;
+                                     frame_buffer_pool_.get())));
+  BufferState& buffer_state = insert_result.first->second;
   DCHECK(buffer_state.HasZeroConsumerHoldCount());
+  if (!insert_result.second)
+    buffer_state.SetFrameFeedbackId(buffer.frame_feedback_id());

[mcasas, 2017/01/30 15:36:34]

This is confusing.  buffer.frame_feedback_id() is used to
set Buffer's |frame_feedback_id_| in l.101, so what's the
point in re-pasting this value if the insert(std::make_pair())
fails? More to the point, how could a construction+
insert(std::make_pair()) fail? (Note that BufferState is a POD,
right? std::is_pod<VideoCaptureController::BufferState>::value
verifies).

[chfremer, 2017/01/30 21:18:27]

Please see PatchSet#2 and let me know if it makes things clearer.

 
   if (state_ == VIDEO_CAPTURE_STATE_STARTED) {
     if (!frame->metadata()->HasKey(VideoFrameMetadata::FRAME_RATE)) {