add SkClipStack::clipEmpty() as an optimized way to say clipDevRect(empty, intersect)
if the caller knows up-front that it wants the clipstact to become empty.
Review URL: https://codereview.appspot.com/6443132

git-svn-id: http://skia.googlecode.com/svn/trunk@5127 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed