GitLab

Avoids downcasting CastDecoderBuffer to DecoderBufferBase in multizone
code.

Bug: internal b/62147653
Test: cast_media_unittests
Change-Id: I4b0fe09bd6aee26c5372405a9052252c39be36e5
Reviewed-on: https://chromium-review.googlesource.com/972429
Commit-Queue: James West <jameswest@chromium.org>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544890}