MediaStreamSource: verify unlocked state when finalizing.

To diagnose an audio thread crash condition, verify that the lock
over audio consumers that MediaStreamSource keeps, isn't held when it is
being finalized. If it is, then the audio thread is active using the
MediaStreamSource object..which is not a well-formed state to be in.

R=
BUG=682945

Review-Url: https://codereview.chromium.org/2741663004
Cr-Commit-Position: refs/heads/master@{#456029}
2 files changed