Fix race condition in FrameBuffer2

Fix race condition in FrameBuffer2

If the frame buffer is cleared while the decoding thread is waiting to acquire
the lock in order to return the |next_frame_it| will be invalidated.

BUG=chromium:679306
Review-Url: https://codereview.webrtc.org/2668743002
Cr-Commit-Position: refs/heads/master@{#16384}
Committed: https://chromium.googlesource.com/external/webrtc/+/1c056254a6b8b6521ad2799c8c705b8bbfb9c210

[philipel, 2017-01-31 16:30:50]

philipel@webrtc.org changed reviewers:
+ stefan@webrtc.org

[stefan-webrtc, 2017-01-31 16:35:07]

lgtm

[philipel, 2017-01-31 16:36:07]

The CQ bit was checked by philipel@webrtc.org

[commit-bot: I haz the power, 2017-01-31 16:36:11]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.webrtc.org/...

[commit-bot: I haz the power, 2017-01-31 17:53:13]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1485880567826500, "parent_rev":
"54340d8e7569633f15c79a6687babdebcf9cc989", "commit_rev":
"1c056254a6b8b6521ad2799c8c705b8bbfb9c210"}

[commit-bot: I haz the power, 2017-01-31 17:53:15]

Description was changed from

==========
Fix race condition in FrameBuffer2

If the frame buffer is cleared while the decoding thread is waiting to acquire
the lock in order to return the |next_frame_it| will be invalidated.

BUG=chromium:679306
==========

to

==========
Fix race condition in FrameBuffer2

If the frame buffer is cleared while the decoding thread is waiting to acquire
the lock in order to return the |next_frame_it| will be invalidated.

BUG=chromium:679306

Review-Url: https://codereview.webrtc.org/2668743002
Cr-Commit-Position: refs/heads/master@{#16384}
Committed:
https://chromium.googlesource.com/external/webrtc/+/1c056254a6b8b6521ad2799c8...
==========

[commit-bot: I haz the power, 2017-01-31 17:53:17]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/external/webrtc/+/1c056254a6b8b6521ad2799c8...