Add GM that exercises SkCanvas::discard()

R=robertphillips@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/252443007

git-svn-id: http://skia.googlecode.com/svn/trunk@14365 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed