Added UMA stat for tracking accidental navigations on double tap.

Adding UMA stat to see the effect of the --disable-click-delay flag
on accidental navigations caused by double tap.

Added two UMA enum histograms, one for when click delays are enabled
and one for disabled. The stats track the first user action within
5 seconds of a double tap gesture. The three possibilities are
"navigate back", "stop navigation", and "no action". No action means
we didn't navigate back or stop load within the 5 seconds.

Note, this only tracks navigations within the same ContentView, if a
navigation opens a new tab, the back/stop for those wont be recorded.
However, in practice this shouldn't make a big difference.

BUG=312735

Review URL: https://codereview.chromium.org/53283003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233676 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233676