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
diff --git a/src/gpu/gl/GrGLCreateNullInterface.cpp b/src/gpu/gl/GrGLCreateNullInterface.cpp
index 105fb0b..fa404ce 100644
--- a/src/gpu/gl/GrGLCreateNullInterface.cpp
+++ b/src/gpu/gl/GrGLCreateNullInterface.cpp
@@ -335,12 +335,15 @@
         functions->fGetStringi = noOpGLGetStringi;
         functions->fGetTexLevelParameteriv = noOpGLGetTexLevelParameteriv;
         functions->fGetUniformLocation = noOpGLGetUniformLocation;
+        functions->fInsertEventMarker = noOpGLInsertEventMarker;
         functions->fLoadIdentity = noOpGLLoadIdentity;
         functions->fLoadMatrixf = noOpGLLoadMatrixf;
         functions->fLineWidth = noOpGLLineWidth;
         functions->fLinkProgram = noOpGLLinkProgram;
         functions->fMatrixMode = noOpGLMatrixMode;
         functions->fPixelStorei = nullGLPixelStorei;
+        functions->fPopGroupMarker = noOpGLPopGroupMarker;
+        functions->fPushGroupMarker = noOpGLPushGroupMarker;
         functions->fQueryCounter = noOpGLQueryCounter;
         functions->fReadBuffer = noOpGLReadBuffer;
         functions->fReadPixels = nullGLReadPixels;