Add UMA stats for AppCacheUpdateJob results.

BUG=343620

Review URL: https://codereview.chromium.org/165613002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251844 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251844
Add latency metric mean_js_touch_scroll_latency for JS touch handler driven scroll

The performance of GestureScrollUpdate driven scroll and JS touch
handler driven scroll can be quite different. So it seems more useful
to have a separate metric for each one.

BUG=246034
TEST=1. smoothness test on tough_scheduling_cases with page-filter=touch_handler_scrolling
        shows result of  mean_js_touch_scroll_latency.
     2. smoothness test on tough_scheduling_cases with page-filter=simpel_text_page
        shows result of  mean_touch_scroll_latency.

Review URL: https://codereview.chromium.org/167343003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251845 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251845