Update screenshot animation from Overview

When invoked from Overview, the screenshot ended up at the wrong
size (since the input bitmap is a different size, coming from the
Recents screenshot). Changing the scale to start at the size of the
input bitmap (as well as starting at the correct location) fixes
this problem.

Bug: 155415994
Fix:155415994
Test: manual; tested from Overview and from chord invocation

Change-Id: I25f2ff982af75ea36da7b3e8e47f93c720101b97