Invalid active window if temporary disabling accessibility for test tools.

If accessibility is enabled and a test tool based on the accessibility APIs
connects to the system we suspend the current accessibility services while
the tool is running (to avoid inteference as the tool is such a service) and
after the tool disconnects we restore the accessibility state. The issue is
that when clearing the accessibility state we were also wrongly clearing the
active window. We are now careful to not clear the active window in such a
case.

It is also possible that the active window was never initilaized before the
tool is run so now it is lazily loaded such that if we do not know which one
it is, we get the one the has input focus. The definition of an active window
is the one that has input focus or the user is touching.

bug:17663432

Change-Id: I8868866a5126c590d3bddad099ababb97978227a