Account for content insets in source rect hint for transition into PiP

- As a part of transitioning into PiP, we remove the content insets, and
  as a result, we also need to adjust the source hint rect for the change
  in insets as well.

Bug: 37418994
Test: Enter PiP from YT, ensure no jump at the end

Change-Id: I74219b05c91d3c8b8466dd8fff4d6dd692f08725