Fix media memory usage reporting after a pipeline suspend.

Fix media memory usage reporting after a pipeline suspend.

This resolves a couple issues:
- Stops the memory usage reporting timer when hidden.
- Clears the audio/video memory PipelineStatistics entries upon
  PipelineImpl completing its suspend.

BUG=592186
TEST=new unittest, manually verify timer stops in bg.

Committed: https://crrev.com/3a7d38f42891b83a503228607435586dc1f55465
Cr-Commit-Position: refs/heads/master@{#379644}

[DaleCurtis, 2016-03-05 02:43:39]

dalecurtis@chromium.org changed reviewers:
+ sandersd@chromium.org

[sandersd (OOO until July 31), 2016-03-07 19:37:52]

lgtm

[DaleCurtis, 2016-03-07 19:43:56]

The CQ bit was checked by dalecurtis@chromium.org

[commit-bot: I haz the power, 2016-03-07 19:44:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1769743002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1769743002/1

[commit-bot: I haz the power, 2016-03-07 21:17:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-03-07 21:18:36]

Description was changed from

==========
Fix media memory usage reporting after a pipeline suspend.

This resolves a couple issues:
- Stops the memory usage reporting timer when hidden.
- Clears the audio/video memory PipelineStatistics entries upon
  PipelineImpl completing its suspend.

BUG=592186
TEST=new unittest, manually verify timer stops in bg.
==========

to

==========
Fix media memory usage reporting after a pipeline suspend.

This resolves a couple issues:
- Stops the memory usage reporting timer when hidden.
- Clears the audio/video memory PipelineStatistics entries upon
  PipelineImpl completing its suspend.

BUG=592186
TEST=new unittest, manually verify timer stops in bg.

Committed: https://crrev.com/3a7d38f42891b83a503228607435586dc1f55465
Cr-Commit-Position: refs/heads/master@{#379644}
==========

[commit-bot: I haz the power, 2016-03-07 21:18:37]

Patchset 1 (id:??) landed as
https://crrev.com/3a7d38f42891b83a503228607435586dc1f55465
Cr-Commit-Position: refs/heads/master@{#379644}