Revert of content/common: Remove use of MessageLoopProxy and deprecated MessageLoop APIs

Revert of content/common: Remove use of MessageLoopProxy and deprecated MessageLoop APIs (patchset #9 id:160001 of https://codereview.chromium.org/1134113002/)

Reason for revert:
Broke the build for CHROMEOS && USE_V4L2_CODEC

Original issue's description:
> content/common: Remove use of MessageLoopProxy and deprecated MessageLoop APIs
>
> This patch was mostly autogenerated with https://codereview.chromium.org/1010073002/.
>
> BUG=465354
>
> Committed: https://crrev.com/adc9b4ed3d797c2990d682a3784d2e892198ce00
> Cr-Commit-Position: refs/heads/master@{#329696}

TBR=sievers@chromium.org,skyostil@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=465354
Committed: https://crrev.com/198257faefbf97d3bca16e65e34c7122b7d03103
Cr-Commit-Position: refs/heads/master@{#329728}

[Evan Stade, 2015-05-13 22:03:22]

Created Revert of content/common: Remove use of MessageLoopProxy and deprecated
MessageLoop APIs

[commit-bot: I haz the power, 2015-05-13 22:05:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1135943005/1

[commit-bot: I haz the power, 2015-05-13 22:08:41]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-13 22:10:30]

Patchset 1 (id:??) landed as
https://crrev.com/198257faefbf97d3bca16e65e34c7122b7d03103
Cr-Commit-Position: refs/heads/master@{#329728}