Compute paint invalidation rects for selection in the space
of the backing GraphicsLayer, not the squashing container
(they are not the same in the presence of layer squashing).

BUG=384963

Review URL: https://codereview.chromium.org/337173003

git-svn-id: svn://svn.chromium.org/blink/trunk@176361 bbb929c8-8fbe-4397-9dbb-9b2b20218538