Okay, new plan for dialogs.

Don't dismiss by default when tapping outside, even for AlertDialog.

If AlertDialog doesn't have any buttons, tapping outside will dismiss it.

Applications can make their own dialogs (or activities looking like
dialogs) can use the existing and new APIs to control this behavior
themselves so that it does the right thing.

Change-Id: I02bfb9161e169de0033200211b3a7ec80080bd83