Merge M50: "Fix media memory usage reporting after a pipeline suspend."

Merge M50: "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.

Review URL: https://codereview.chromium.org/1769743002

Cr-Commit-Position: refs/heads/master@{#379644}
(cherry picked from commit 3a7d38f42891b83a503228607435586dc1f55465)

Committed: https://chromium.googlesource.com/chromium/src/+/b6a32ade861a645226d2a436b5fbfed4133129ed

[DaleCurtis, 2016-03-18 23:54:55]

Description was changed from

==========
Merge M50: "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.

Review URL: https://codereview.chromium.org/1769743002

Cr-Commit-Position: refs/heads/master@{#379644}
(cherry picked from commit 3a7d38f42891b83a503228607435586dc1f55465)
==========

to

==========
Merge M50: "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.

Review URL: https://codereview.chromium.org/1769743002

Cr-Commit-Position: refs/heads/master@{#379644}
(cherry picked from commit 3a7d38f42891b83a503228607435586dc1f55465)

Committed:
https://chromium.googlesource.com/chromium/src/+/b6a32ade861a645226d2a436b5fb...
==========

[DaleCurtis, 2016-03-18 23:54:56]

Committed patchset #1 (id:1) manually as
b6a32ade861a645226d2a436b5fbfed4133129ed (tree was closed).