Add Xfermode bench. Also clear before rendering in bench (rather than after).

Author: bsalomon@google.com

Reviewed By: robertphillips@google.com

Review URL: https://chromiumcodereview.appspot.com/13334011

git-svn-id: http://skia.googlecode.com/svn/trunk@8454 2bbb7eff-a529-9590-31e7-b0007b416f81
5 files changed