SkClipStack::isRRect succeeds if stack is  an intersection of rects.

This helps enable optimizations that rely on the entire clip reducing
to a single rectangle, such as converting a drawRect to a clear.

Bug: b/122296071

Change-Id: I1fea4565644280d57610f8585b76babb557301d8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/209382
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
2 files changed