Renamed perf_tools -> metrics, and *_metrics.py -> *_metric.py

BUG=

Review URL: https://chromiumcodereview.appspot.com/21205005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@215170 0039d316-1c4b-4281-b951-d872f2087c98
24 files changed