Add a way for the gpu veto to report back the reason why it said no BUG=2334 [email protected] Author: [email protected] Review URL: https://codereview.chromium.org/301423002 git-svn-id: http://skia.googlecode.com/svn/trunk@15012 2bbb7eff-a529-9590-31e7-b0007b416f81