Reland of Add a flags field to video timing extension.

webrtc/common_video/video_frame.cc

Index: webrtc/common_video/video_frame.cc
diff --git a/webrtc/common_video/video_frame.cc b/webrtc/common_video/video_frame.cc
index e01aa01e1898107a3df0d4f520423653894b7c73..8678700e9ab122f1ba48e7520e282564fb74aadf 100644
--- a/webrtc/common_video/video_frame.cc
+++ b/webrtc/common_video/video_frame.cc
@@ -49,7 +49,6 @@ EncodedImage::EncodedImage(uint8_t* buffer, size_t length, size_t size)
 
 void EncodedImage::SetEncodeTime(int64_t encode_start_ms,
                                 int64_t encode_finish_ms) const {
-    timing_.is_timing_frame = true;
     timing_.encode_start_ms = encode_start_ms;
     timing_.encode_finish_ms = encode_finish_ms;
 }