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 3de5c333fb52d3aef40c17eb2cb7c4d0c3606d5b..f4a0ee975f1923d9db8206018808e715bfc3566f 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::OK;
   };