Fix PopupWindowTest#testShowAtLocation to Support 0 Padding

Bug 2941912

Change the assertion that depended upon the popup window's theme
having > 0 padding. Removing the PopupWindow theme's background to
simulate a lack of padding causes this test to fail unless the
assertions allow zero padding.

Change-Id: I9e2aae710526182b03b9637a29c75cf01c9cbc4d
1 file changed