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

Review URL: https://codereview.chromium.org/942583005

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#317299}

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