Adding back UMA stat tracking on back navigation.

Added back double-tap click delay UMA stat tracking that was removed in
https://codereview.chromium.org/82693007

BUG=

Review URL: https://codereview.chromium.org/176973003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253376 0039d316-1c4b-4281-b951-d872f2087c98
Clamp keyboard context menu locations to visible ancestor areas.

Previously, the menu could anchor outside an ancestor view.
See before/after pics at http://crbug.com/330496

BUG=330496
TEST=Keyboard-triggered context menus (via the Menu key or Shift+F10) show in reasonable locations.
R=sky@chromium.org

Review URL: https://codereview.chromium.org/179053002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253377 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253377