Revert of Lazily initialize MessageLoop for faster thread startup

Revert of Lazily initialize MessageLoop for faster thread startup (patchset #28 id:870001 of https://codereview.chromium.org/1011683002/)

Reason for revert:
This introduced flaky assertion failure on some tests  http://crbug.com/485157

Original issue's description:
> Lazily initialize MessageLoop for faster thread startup
>
> Summary of the change and background discussion:
> https://docs.google.com/a/chromium.org/document/d/1o1vUUOjX3tC7pV5-nxchaGtElo4NwtzKOAb4Zm09ezw/edit#
>
> This implements approach 1 in the doc.
> Approach 2: https://codereview.chromium.org/1086663002/
> Approach 3: https://codereview.chromium.org/1058603004/
>
> Discussion thread:
> https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/2t6lB8hUgYw
>
> BUG=465458
>
> Committed: https://crrev.com/f1f70cb5ebe24d85c575396f026a415ed0fe9afc
> Cr-Commit-Position: refs/heads/master@{#328347}

TBR=dalecurtis@chromium.org,rvargas@chromium.org,tommi@chromium.org,mark@chromium.org,thakis@chromium.org,danakj@chromium.org,pauljensen@chromium.org,jam@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=465458
Committed: https://crrev.com/448203e533c5bdb3ba11df536d100c38d15b6b51
Cr-Commit-Position: refs/heads/master@{#328674}

[kinuko, 2015-05-07 01:26:50]

Created Revert of Lazily initialize MessageLoop for faster thread startup

[commit-bot: I haz the power, 2015-05-07 01:27:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1122383003/1

[commit-bot: I haz the power, 2015-05-07 01:30:07]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-07 01:31:17]

Patchset 1 (id:??) landed as
https://crrev.com/448203e533c5bdb3ba11df536d100c38d15b6b51
Cr-Commit-Position: refs/heads/master@{#328674}