telemetry: Fix smoothness metric and repaint measurement

Completing revert of r256661 (https://codereview.chromium.org/170183004).

https://codereview.chromium.org/198063007/ left some issues in repaint
measurement and smoothness metric, that are fixed by this patch.

TBR=tonyg@chromium.org
BUG=352215
NOTRY=True

Review URL: https://codereview.chromium.org/199753002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256968 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256968