Move GrGLExtensions from GrGLContextInfo to GrGLInterface

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

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/140823003

git-svn-id: http://skia.googlecode.com/svn/trunk@13118 2bbb7eff-a529-9590-31e7-b0007b416f81
18 files changed