Revert of Make sure MessagePortService is used in a thread safe manner.

Revert of Make sure MessagePortService is used in a thread safe manner. (patchset #4 id:80001 of https://codereview.chromium.org/937503003/)

Reason for revert:
This CL is suspected to cause the Win7 test (dbg) failures.

Original issue's description:
> Added DCHECKs to all public methods of MessagePortService to make sure it is used in a thread safe manner.
>
> BUG=459115
>
> Committed: https://crrev.com/c2d9552dde5a7dd05dc63e744c71f497f0120306
> Cr-Commit-Position: refs/heads/master@{#317178}

TBR=creis@chromium.org,sgurun@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=459115
Committed: https://crrev.com/60583adc54a6b043dc0b812f10869801eb0da0b4
Cr-Commit-Position: refs/heads/master@{#317299}

[kaliamoorthi, 2015-02-20 12:19:55]

Created Revert of Make sure MessagePortService is used in a thread safe manner.

[commit-bot: I haz the power, 2015-02-20 12:20:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/942583005/1

[commit-bot: I haz the power, 2015-02-20 12:21:12]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-20 12:22:10]

Patchset 1 (id:??) landed as
https://crrev.com/60583adc54a6b043dc0b812f10869801eb0da0b4
Cr-Commit-Position: refs/heads/master@{#317299}

[kaliamoorthi, 2015-02-20 14:07:25]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/947483002/ by kaliamoorthi@chromium.org.

The reason for reverting is: This does not seem to cause the problem..