events: Move gestures out of ui/base/ into ui/events/.

BUG=none
R=ben@chromium.org

Review URL: https://codereview.chromium.org/24413002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225109 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225109