PopupWindow: Be more careful with FLAG_LAYOUT_NO_LIMITS

If we intend to clip to the screen we can't pass NO_LIMITS.
Luckily the default behavior for LAYOUT_IN_PARENT_FRAME is to not
clip to the parent frame, so we don't have to do anything except
update our local flag we use for explicit size calculations.

Bug: 28194524
Change-Id: I1465efce7f5412cf646bccd83e23a4b049f4dbc4