events: Move all references to ui/base/ from ui/events.

Notable changes:
  * Move TouchFactory from ui/base/ into ui/events/x/.
  * Split out some switches from ui/base/ into ui/events/.
  * Move SequentialIDGenerator from ui/base/ into ui/gfx/.

BUG=none
R=ben@chromium.org

Review URL: https://codereview.chromium.org/24692003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225367 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225367