cc: Add TRACE_EVENTs to SingleThreadProxy

This adds traces to entry points in SingleThreadProxy that have
analogous trace events in the ThreadProxy. Also add trace points
along the critical CompositeImmediately -> CommitAndComposite ->
DoCommit/DoComposite code path.

R=enne
BUG=339248

Review URL: https://codereview.chromium.org/149053006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247874 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247874