When accessibility on cannot click on a view covered by a HorizontalScrollView

In accessibility mode we send down and up events activate a view. We will later
switch to accessibility actions but for now as a bridge-gap we compute a point on
the screen where to click for activating the view. The heuristic we use has edge
cases such as a view that handles all touch events but does not have any listeners.
In this case we do not ignore the target view's area covered by a view that handles
all touch events. As a result we click on the wrong target. While we cannot solve
this generically, in the case of standard components such as HorizontalScrollView
we can.

bug:18612258

Change-Id: If8482aac0d0ea53c5c90367d099d1b8d3a4559ed