Allow each WGC3D subclass to determine the correct GrGLInterface for its GrContext.

webkit/glue/gl_bindings_skia_cmd_buffer.h

Index: webkit/glue/gl_bindings_skia_cmd_buffer.h
===================================================================
--- webkit/glue/gl_bindings_skia_cmd_buffer.h	(revision 98420)
+++ webkit/glue/gl_bindings_skia_cmd_buffer.h	(working copy)
@@ -6,11 +6,13 @@
 #define WEBKIT_GLUE_GL_BINDINGS_SKIA_CMD_BUFFER_H_
 #pragma once
 
+struct GrGLInterface;
+
 namespace webkit_glue {
 
 // The GPU back-end for skia requires pointers to GL functions. This function
 // binds skia-gpu to the cmd buffers GL.
-void BindSkiaToCommandBufferGL();
+GrGLInterface* GetCommandBufferSkiaGLBinding();
 
 }  // namespace webkit_glue