Fix WindowFrameTest error.

It appears somehow we are using real display sizes and it varies from
device to device. This itself is somewhat concerning, but easy enough
to handle. If you look at the line before the modified lines
it seems like this is what I meant to do initially but somehow it didn't happen.

Test: bit FrameworksServicesTests:com.android.server.wm.WindowFrameTests
Fixes: 35197592
Change-Id: I05880ba95a8ee3b790fb14daf00c878b4f85095c