cc: Add failure info to LTHAnimationTest...WithoutActiveTree

This has flaked with the active tree assert being wrong twice and it'd
be good to understand which commit this was happening on to better
diagnose this problem.

BUG=312952

Review URL: https://codereview.chromium.org/50713005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232008 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232008