Revert of [media] Replace MessageLoopProxy usage with ThreadTaskRunnerHandle

Revert of [media] Replace MessageLoopProxy usage with ThreadTaskRunnerHandle (patchset #3 id:40001 of https://codereview.chromium.org/1108773002/)

Reason for revert:
see https://code.google.com/p/chromium/issues/detail?id=481632

Original issue's description:
> Replace MessageLoopProxy usage with ThreadTaskRunnerHandle in src/media.
>
> MessageLoopProxy is deprecated.
> This basically does a search and replace:
>
> MessageLoopProxy::current() -> ThreadTaskRunnerHandle::Get().
>
> BUG=391045
>
> Committed: https://crrev.com/902e992a9b6447028bf8d4f3540892c425984b8f
> Cr-Commit-Position: refs/heads/master@{#327075}

TBR=anujk.sharma@samsung.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=391045
Committed: https://crrev.com/84a3918452ae67b24bc60acdf7abd7b226879a5e
Cr-Commit-Position: refs/heads/master@{#327142}

[xhwang, 2015-04-27 21:39:35]

Created Revert of [media] Replace MessageLoopProxy usage with
ThreadTaskRunnerHandle

[commit-bot: I haz the power, 2015-04-27 21:40:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1105163004/1

[commit-bot: I haz the power, 2015-04-27 21:42:22]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-27 21:43:56]

Patchset 1 (id:??) landed as
https://crrev.com/84a3918452ae67b24bc60acdf7abd7b226879a5e
Cr-Commit-Position: refs/heads/master@{#327142}