add isRect() check to AAClip, to detect if a soft-clip is really just an irect

taken from (https://codereview.chromium.org/445233006/)

fix: don't assume that the first yoffset is 0, since we may have performed a translate and not
re-alloced our data.

This reverts commit 0aeea6d344f12e35e29a79f4bbc48af88f913204.

TBR=

Author: reed@google.com

Review URL: https://codereview.chromium.org/443353004
5 files changed