Fix keyboard not showing for global search on Dream. Rather than trying to

call the hidden showSoftInputUnchecked method to show the IME in SearchDialog#show(),
override onWindowFocusChanged in our subclass of AutoCompleteTextView so that whenever
it gets focus, we call the public showSoftInput method, passing in the ACTV, which is
the correct way to do this.

This fixes http://b/1930989.