Let VideoRenderFrames::FrameToRender return rtc::Optional

webrtc/common_video/video_render_frames.cc

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 35 matching lines @@
     WEBRTC_TRACE(kTraceWarning, kTraceVideoRenderer, -1,
                  "%s: frame too long into the future, timestamp=%u.",
                  __FUNCTION__, new_frame.timestamp());
     return -1;
   }
 
   incoming_frames_.push_back(new_frame);
   return static_cast<int32_t>(incoming_frames_.size());
 }
 
-VideoFrame VideoRenderFrames::FrameToRender() {
-  VideoFrame render_frame;
+rtc::Optional<VideoFrame> VideoRenderFrames::FrameToRender() {
+  rtc::Optional<VideoFrame> render_frame;
   // Get the newest frame that can be released for rendering.
   while (!incoming_frames_.empty() && TimeToNextFrameRelease() <= 0) {
-    render_frame = incoming_frames_.front();
+    render_frame = rtc::Optional<VideoFrame>(incoming_frames_.front());
     incoming_frames_.pop_front();
   }
   return render_frame;
 }
 
 int32_t VideoRenderFrames::ReleaseAllFrames() {
   incoming_frames_.clear();
   return 0;
 }
 
@@ skipping 15 matching lines @@
                  -1, "%s(%d): Invalid argument.", __FUNCTION__,
                  render_delay);
     return -1;
   }
 
   render_delay_ms_ = render_delay;
   return 0;
 }
 
 }  // namespace webrtc