Revert of Trace MessageLoop::RunTask execution (patchset #2 id:20001 of https://codereview.chromium.org/1225333002/)

Reason for revert:
Regressed perf on Nexus 7
BUG=509982,508005

Original issue's description:
> Trace MessageLoop::RunTask execution
>
> Previously, we were only issuing trace events around the task execution
> within TaskAnnotator::RunTask. However, this does not include time spent
> in observers (see bug for details on how it bites).
>
> BUG=508005
>
> Committed: https://crrev.com/87a2c639ff073ed3194a788ee1eaf82aabe77bab
> Cr-Commit-Position: refs/heads/master@{#338492}

[email protected],[email protected],[email protected]
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=508005

Review URL: https://codereview.chromium.org/1234573005

Cr-Commit-Position: refs/heads/master@{#338676}
1 file changed