[gin] Introduce Wrappable::GetObjectTemplate

mojo/apps/js/bindings/gl/context.h

Index: mojo/apps/js/bindings/gl/context.h
diff --git a/mojo/apps/js/bindings/gl/context.h b/mojo/apps/js/bindings/gl/context.h
index 40203c317cb559ddc3fa6864fc99c9fd490d29c4..7241fc077f75887884d7dcb635c4bdd50e6af0a0 100644
--- a/mojo/apps/js/bindings/gl/context.h
+++ b/mojo/apps/js/bindings/gl/context.h
@@ -30,8 +30,6 @@ class Context : public gin::Wrappable<Context> {
 
   static gin::Handle<Context> Create(v8::Isolate* isolate, uint64_t encoded,
                                      int width, int height);
-  static v8::Handle<v8::ObjectTemplate> GetObjectTemplate(v8::Isolate* isolate);
-
   static gin::Handle<Shader> CreateShader(const gin::Arguments& arguments,
                                           GLenum type);
   static void ShaderSource(gin::Handle<Shader> shader,
@@ -40,6 +38,9 @@ class Context : public gin::Wrappable<Context> {
                             gin::Handle<Shader> shader);
 
  private:
+  friend class gin::Wrappable<Context>;
+  static v8::Local<v8::ObjectTemplate> GetObjectTemplate(v8::Isolate* isolate);
+
   Context(uint64_t encoded, int width, int height);
 
   uint64_t encoded_;