Create standalone GestureEventFilter unit tests

Move GestureEventFilter-related tests from the general router tests to the more
specific GestureEventFilterTest. Create GestureEventFilterClient and
TouchpadTapSuppressionControllerClient interfaces to remove explicit InputRouter
dependencies.

BUG=301807,302592

Review URL: https://codereview.chromium.org/26376002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227673 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227673