Replace GrGLInterface's function pointers with std::functions

include/gpu/gl/GrGLExtensions.h

Index: include/gpu/gl/GrGLExtensions.h
diff --git a/include/gpu/gl/GrGLExtensions.h b/include/gpu/gl/GrGLExtensions.h
index d64a268a46be24d107bde46e4593251b07ea6791..fe3187057c95b4e145b3d29c2e8a1fe478fac87a 100644
--- a/include/gpu/gl/GrGLExtensions.h
+++ b/include/gpu/gl/GrGLExtensions.h
@@ -39,10 +39,10 @@ public:
      * NULL if on desktop GL with version 3.0 or higher. Otherwise it will fail.
      */
     bool init(GrGLStandard standard,
-              GrGLGetStringProc getString,
-              GrGLGetStringiProc getStringi,
-              GrGLGetIntegervProc getIntegerv,
-              GrEGLQueryStringProc queryString = nullptr,
+              GrGLFunction<GrGLGetStringProc> getString,
+              GrGLFunction<GrGLGetStringiProc> getStringi,
+              GrGLFunction<GrGLGetIntegervProc> getIntegerv,
+              GrGLFunction<GrEGLQueryStringProc> queryString = nullptr,
               GrEGLDisplay eglDisplay = nullptr);
 
     bool isInitialized() const { return fInitialized; }