This CL adds a lock to stashed_images_ in MultiplexEncoderAdapter.
Without lock, it is possible that different threads acts on
stashed_images_ simultaneously and leads to crash.
Bug: webrtc:8965
Change-Id: I887861092d185c3bd6047eb529d8c1cf57fa4648
Reviewed-on: https://webrtc-review.googlesource.com/59260
Reviewed-by: Emircan Uysaler <emircan@webrtc.org>
Commit-Queue: Qiang Chen <qiangchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#22261}
6d30631f01