Add a flags field to video timing extension.

webrtc/modules/video_coding/generic_encoder_unittest.cc

Index: webrtc/modules/video_coding/generic_encoder_unittest.cc
diff --git a/webrtc/modules/video_coding/generic_encoder_unittest.cc b/webrtc/modules/video_coding/generic_encoder_unittest.cc
index eec5b98bbabbc9b362056726ca3f35fbb111c77d..f3ca0883a114fc380a57cadab5fdf945f4be4db3 100644
--- a/webrtc/modules/video_coding/generic_encoder_unittest.cc
+++ b/webrtc/modules/video_coding/generic_encoder_unittest.cc
@@ -31,7 +31,8 @@ class FakeEncodedImageCallback : public EncodedImageCallback {
   Result OnEncodedImage(const EncodedImage& encoded_image,
                         const CodecSpecificInfo* codec_specific_info,
                         const RTPFragmentationHeader* fragmentation) override {
-    last_frame_was_timing_ = encoded_image.timing_.is_timing_frame;
+    last_frame_was_timing_ =
+        encoded_image.timing_.flags != TimingFrameFlags::kInvalid;
     return Result(Result::OK);
   };