Make internal_source argument to FrameEncodeMetadataWriter::OnEncoderInit optional

Bug: webrtc:12875
Change-Id: I74afff080c4965fe51750c7016abfd2c734dcc65
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/237222
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35308}
diff --git a/video/frame_encode_metadata_writer.h b/video/frame_encode_metadata_writer.h
index 8847145..541ed98 100644
--- a/video/frame_encode_metadata_writer.h
+++ b/video/frame_encode_metadata_writer.h
@@ -28,7 +28,7 @@
   explicit FrameEncodeMetadataWriter(EncodedImageCallback* frame_drop_callback);
   ~FrameEncodeMetadataWriter();
 
-  void OnEncoderInit(const VideoCodec& codec, bool internal_source);
+  void OnEncoderInit(const VideoCodec& codec, bool internal_source = false);
   void OnSetRates(const VideoBitrateAllocation& bitrate_allocation,
                   uint32_t framerate_fps);