This CL changes some types in MultiplexImage and MultiplexImageComponent. Also, adds unit test coverage in TestMultiplexAdapter for these structs. Bug: webrtc:7671 Change-Id: I832d0466dc67d3b6b7fa0d3fb76f02c0190e474f Reviewed-on: https://webrtc-review.googlesource.com/44081 Commit-Queue: Emircan Uysaler <emircan@webrtc.org> Reviewed-by: Qiang Chen <qiangchen@chromium.org> Cr-Commit-Position: refs/heads/master@{#21770}