gin: Add ability to install call-as-function handlers on gin::Wrappable

gin/object_template_builder.h

Index: gin/object_template_builder.h
diff --git a/gin/object_template_builder.h b/gin/object_template_builder.h
index 6367b71245c81dbb70b12c926811d3a63e6d0ed8..768f4c8551c4f16b5b003ed119d83322ee36fe00 100644
--- a/gin/object_template_builder.h
+++ b/gin/object_template_builder.h
@@ -27,6 +27,11 @@ struct CallbackTraits {
                                                          T callback) {
     return CreateFunctionTemplate(isolate, base::Bind(callback));
   }
+  static void SetAsFunctionHandler(v8::Isolate* isolate,
+                                   v8::Local<v8::ObjectTemplate> tmpl,
+                                   T callback) {
+    CreateFunctionHandler(isolate, tmpl, base::Bind(callback));
+  }
 };
 
 // Specialization for base::Callback.
@@ -36,6 +41,11 @@ struct CallbackTraits<base::Callback<T> > {
       v8::Isolate* isolate, const base::Callback<T>& callback) {
     return CreateFunctionTemplate(isolate, callback);
   }
+  static void SetAsFunctionHandler(v8::Isolate* isolate,
+                                   v8::Local<v8::ObjectTemplate> tmpl,
+                                   const base::Callback<T>& callback) {
+    CreateFunctionHandler(isolate, tmpl, callback);
+  }
 };
 
 // Specialization for member function pointers. We need to handle this case
@@ -50,6 +60,12 @@ struct CallbackTraits<T, typename base::enable_if<
     return CreateFunctionTemplate(isolate, base::Bind(callback),
                                   HolderIsFirstArgument);
   }
+  static void SetAsFunctionHandler(v8::Isolate* isolate,
+                                   v8::Local<v8::ObjectTemplate> tmpl,
+                                   T callback) {
+    CreateFunctionHandler(
+        isolate, tmpl, base::Bind(callback), HolderIsFirstArgument);
+  }
 };
 
 // This specialization allows people to construct function templates directly if
@@ -103,6 +119,11 @@ class GIN_EXPORT ObjectTemplateBuilder {
                            CallbackTraits<T>::CreateTemplate(isolate_, getter),
                            CallbackTraits<U>::CreateTemplate(isolate_, setter));
   }
+  template<typename T>
+  ObjectTemplateBuilder& SetCallAsFunctionHandler(const T& callback) {
+    CallbackTraits<T>::SetAsFunctionHandler(isolate_, template_, callback);
+    return *this;
+  }
 
   v8::Local<v8::ObjectTemplate> Build();