Add a flags field to video timing extension.

webrtc/common_video/include/video_frame.h

Index: webrtc/common_video/include/video_frame.h
diff --git a/webrtc/common_video/include/video_frame.h b/webrtc/common_video/include/video_frame.h
index 10dfb47cc94e705ed9062d63e4dbdf5cfea18efb..398e89c83eda0a24c561e59aa0fa69fcca48290c 100644
--- a/webrtc/common_video/include/video_frame.h
+++ b/webrtc/common_video/include/video_frame.h
@@ -36,7 +36,6 @@ class EncodedImage {
       : _buffer(buffer), _length(length), _size(size) {}
 
   void 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;
   }
@@ -72,7 +71,7 @@ class EncodedImage {
 
   // Timing information should be updatable on const instances.
   mutable struct Timing {
-    bool is_timing_frame = false;
+    uint8_t flags = TimingFrameFlags::kInvalid;
     int64_t encode_start_ms = 0;
     int64_t encode_finish_ms = 0;
     int64_t packetization_finish_ms = 0;