Revert 251178 "Trace event micro-optimization: use finer grained..."
due to data races raised on the tsan v2 bot.

BUG=343802

> Trace event micro-optimization: use finer grained lock.
> 
> GetCategoryGroupEnabledInternal is a hotspot.
> It traverses an append-only list, so it's safe to use a finer-grained lock,
> and avoid it altogether for the "fast path", i.e., when the category is
> already known.
> 
> BUG=
> 
> Review URL: https://codereview.chromium.org/144423009

TBR=bulach@chromium.org

Review URL: https://codereview.chromium.org/163613006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251262 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251262