BlurTests: use screenshot of activity bounds

The tests previously failed on multi-screen (foldable) devices because
of the instrumentation screenshot capturing the entire display, causing
the tests to use an incorrect screen width when comparing pixel colors.
This commit fixes the issue by limiting the screenshot Bitmap to the
BackgroundImageActivity's bounds.

Signed-off-by: Andrei Sfartz <ansfartz@microsoft.com>
Change-Id: I3109cd497b18688807633059379c1f90c8b9e921
2 files changed