telemetry: Add new rendering benchmarks.

Adding rasterize_and_record.top_25, rasterize_and_record.key_mobile_sites, and
smoothness.key_mobile_sites benchmarks in preparation for rebase of https://codereview.chromium.org/25548005/

R=tonyg@chromium.org
BUG=295874

Review URL: https://codereview.chromium.org/29913002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230328 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230328