Chromecast: use weak pointers for AvPipelineImpl callbacks on CMA thread.

Chromecast: use weak pointers for AvPipelineImpl callbacks on CMA thread.

Without this, there can be circular references keeping AvPipelineImpl
alive after media pipeline destruction.

R=lcwu@chromium.org,halliwell@chromium.org
BUG=internal b/19643195

Committed: https://crrev.com/b1b1e8c6c1aa269142344ed2b2937c9ddb230bee
Cr-Commit-Position: refs/heads/master@{#320409}

[gunsch, 2015-03-12 19:33:53]

On 2015/03/12 19:29:54, gunsch wrote:

Verified by successive re-castings (including with protected content to avoid
regressions on previous issues) and watching /dev/shm. Pipeline is clearly freed
now.

Couple notes, per my understanding of the code / talking with Luke:
* AvPipelineImpl references in callbacks should be weak-ptrs, to avoid
unnecessarily keeping AvPipelineImpl alive.
* OnCdmDestroyed callback reference still needs to be the ref-counted reference,
since weak-ptr is not thread-safe.
* AvPipelineImpl::Finalize removes the callbacks (and BrowserCdmCast callbacks
are thread-safe), so there is no condition where OnCdmDestroyed could be called
on an invalid AvPipelineImpl.

[halliwell, 2015-03-12 21:01:45]

On 2015/03/12 19:33:53, gunsch wrote:
> On 2015/03/12 19:29:54, gunsch wrote:
> 
> Verified by successive re-castings (including with protected content to avoid
> regressions on previous issues) and watching /dev/shm. Pipeline is clearly
freed
> now.
> 
> Couple notes, per my understanding of the code / talking with Luke:
> * AvPipelineImpl references in callbacks should be weak-ptrs, to avoid
> unnecessarily keeping AvPipelineImpl alive.
> * OnCdmDestroyed callback reference still needs to be the ref-counted
reference,
> since weak-ptr is not thread-safe.
> * AvPipelineImpl::Finalize removes the callbacks (and BrowserCdmCast callbacks
> are thread-safe), so there is no condition where OnCdmDestroyed could be
called
> on an invalid AvPipelineImpl.

lgtm

[lcwu1, 2015-03-12 23:54:19]

lgtm

[gunsch, 2015-03-13 00:02:37]

The CQ bit was checked by gunsch@chromium.org

[commit-bot: I haz the power, 2015-03-13 00:03:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1005703002/1

[commit-bot: I haz the power, 2015-03-13 00:06:32]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-13 00:07:21]

Patchset 1 (id:??) landed as
https://crrev.com/b1b1e8c6c1aa269142344ed2b2937c9ddb230bee
Cr-Commit-Position: refs/heads/master@{#320409}