Make GrGLInterface be context-specific on all platforms

BUG=skia:2042
R=robertphillips@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/137753005

git-svn-id: http://skia.googlecode.com/svn/trunk@13097 2bbb7eff-a529-9590-31e7-b0007b416f81
7 files changed