Fix cull nesting assertion.

Cull rects are in local coordinates and cannot be compared directly.

No wonder it was so hard enforcing this in Blink :o

This moves the validation logic into SkCanvas, using a device-space
cull stack (debug build only).

There are still some Blink bugs causing violations, so for now I'd like
to keep this as an error message only.

R=reed@google.com, robertphillips@google.com

Author: fmalita@chromium.org

Review URL: https://codereview.chromium.org/200923008

git-svn-id: http://skia.googlecode.com/svn/trunk@13885 2bbb7eff-a529-9590-31e7-b0007b416f81
3 files changed