Make tap gesture ignore its ack disposition.

BUG=302852,275611
TEST=ImmediateInputRouterTest.GestureTypesIgnoringAck

Review URL: https://codereview.chromium.org/84653006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243713 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243713