Add FakeVp8Decoder that parse width and height from the payload. Add unit test for testing that width and height is set when decoding frames. Bug: none Change-Id: Ifbfff4f62f99625309ce0ef21cf89c76448769d8 Reviewed-on: https://webrtc-review.googlesource.com/c/103140 Commit-Queue: Per Kjellander <perkj@webrtc.org> Reviewed-by: Sebastian Jansson <srte@webrtc.org> Reviewed-by: Erik Språng <sprang@webrtc.org> Cr-Commit-Position: refs/heads/master@{#25038}