Add hooks for GL_EXT_debug_marker in gpu

BUG=skia:
R=bsalomon@google.com

Author: egdaniel@google.com

Review URL: https://codereview.chromium.org/174123003

git-svn-id: http://skia.googlecode.com/svn/trunk@13538 2bbb7eff-a529-9590-31e7-b0007b416f81
23 files changed