SkRectShaderImageFilter: add a workaround for the zero-sized rects currently passed by Blink.

BUG=306488
R=robertphillips@google.com, robertphillips

Review URL: https://codereview.chromium.org/26799004

git-svn-id: http://skia.googlecode.com/svn/trunk@11733 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed