Add API to SendActionToFirstResponder.

It's important to bind application menu items to curtain actions of
first responder, like 'quit', 'minimize', 'copy' etc. This API gives
developers ability to do most of them in javascript.

browser/api/atom_api_menu.h

@@ -69,6 +69,8 @@ class Menu : public EventEmitter,
   static v8::Handle<v8::Value> Popup(const v8::Arguments &args);
 
   static v8::Handle<v8::Value> SetApplicationMenu(const v8::Arguments &args);
+  static v8::Handle<v8::Value> SendActionToFirstResponder(
+      const v8::Arguments &args);
 
   DISALLOW_COPY_AND_ASSIGN(Menu);
 };