Merge M52: "Invalidate FFmpegDemuxer WeakPtrs on the right thread."

Merge M52: "Invalidate FFmpegDemuxer WeakPtrs on the right thread."

Previously these may not have been invalidated until the class is
destructed on the render thread, when they are bound to the media
thread.

BUG=618625
TEST=none

Review-Url: https://codereview.chromium.org/2084643003
Cr-Commit-Position: refs/heads/master@{#400835}
(cherry picked from commit 9053fbc0d49919dd9e48b86d7df820562e845d80)

Committed: https://chromium.googlesource.com/chromium/src/+/0827287fdad94c10746403cdc271c06970a1dd15

[DaleCurtis, 2016-06-22 01:22:02]

Description was changed from

==========
Merge M52: "Invalidate FFmpegDemuxer WeakPtrs on the right thread."

Previously these may not have been invalidated until the class is
destructed on the render thread, when they are bound to the media
thread.

BUG=618625
TEST=none

Review-Url: https://codereview.chromium.org/2084643003
Cr-Commit-Position: refs/heads/master@{#400835}
(cherry picked from commit 9053fbc0d49919dd9e48b86d7df820562e845d80)
==========

to

==========
Merge M52: "Invalidate FFmpegDemuxer WeakPtrs on the right thread."

Previously these may not have been invalidated until the class is
destructed on the render thread, when they are bound to the media
thread.

BUG=618625
TEST=none

Review-Url: https://codereview.chromium.org/2084643003
Cr-Commit-Position: refs/heads/master@{#400835}
(cherry picked from commit 9053fbc0d49919dd9e48b86d7df820562e845d80)

Committed:
https://chromium.googlesource.com/chromium/src/+/0827287fdad94c10746403cdc271...
==========

[DaleCurtis, 2016-06-22 01:22:04]

Committed patchset #1 (id:1) manually as
0827287fdad94c10746403cdc271c06970a1dd15.