FrameBuffer::NextFrame now return pair<frame, reason>.

webrtc/modules/video_coding/frame_buffer2.cc

Index: webrtc/modules/video_coding/frame_buffer2.cc
diff --git a/webrtc/modules/video_coding/frame_buffer2.cc b/webrtc/modules/video_coding/frame_buffer2.cc
index dab783254684e2ff140ed598bd3fdc022f9dbd57..813b15bdb1c7c96afbb217e437139b8e2d54d350 100644
--- a/webrtc/modules/video_coding/frame_buffer2.cc
+++ b/webrtc/modules/video_coding/frame_buffer2.cc
@@ -52,7 +52,8 @@ FrameBuffer::FrameBuffer(Clock* clock,
       stopped_(false),
       protection_mode_(kProtectionNack) {}
 
-std::unique_ptr<FrameObject> FrameBuffer::NextFrame(int64_t max_wait_time_ms) {
+rtc::Optional<std::unique_ptr<FrameObject>>
+FrameBuffer::NextFrame(int64_t max_wait_time_ms) {
   int64_t latest_return_time = clock_->TimeInMilliseconds() + max_wait_time_ms;
   int64_t now = clock_->TimeInMilliseconds();
   int64_t wait_ms = max_wait_time_ms;
@@ -63,7 +64,7 @@ std::unique_ptr<FrameObject> FrameBuffer::NextFrame(int64_t max_wait_time_ms) {
       rtc::CritScope lock(&crit_);
       frame_inserted_event_.Reset();
       if (stopped_)
-        return std::unique_ptr<FrameObject>();
+        return rtc::Optional<std::unique_ptr<FrameObject>>();
 
       now = clock_->TimeInMilliseconds();
       wait_ms = max_wait_time_ms;
@@ -115,9 +116,9 @@ std::unique_ptr<FrameObject> FrameBuffer::NextFrame(int64_t max_wait_time_ms) {
         decoded_frames_.insert(next_frame_it->first);
         std::unique_ptr<FrameObject> frame = std::move(next_frame_it->second);
         frames_.erase(frames_.begin(), ++next_frame_it);
-        return frame;
+        return rtc::Optional<std::unique_ptr<FrameObject>>(std::move(frame));
       } else {
-        return std::unique_ptr<FrameObject>();
+        return rtc::Optional<std::unique_ptr<FrameObject>>(nullptr);
       }
     }
   }