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

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251178 0039d316-1c4b-4281-b951-d872f2087c98
Mojo: Prefix user-defined parameter names to avoid conflicts

BUG=342543

Review URL: https://codereview.chromium.org/163113002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251179 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251179