Pass synchronous messages by JSON string.

We are going to use IPC_MESSAGE_HANDLER_DELAY_REPLY to handle
synchronous messages but DictionaryValue is not copyable, so we pass the
JSON string instead.

browser/api/atom_api_event.h

@@ -5,6 +5,8 @@
 #ifndef ATOM_BROWSER_ATOM_API_EVENT_H_
 #define ATOM_BROWSER_ATOM_API_EVENT_H_
 
+#include <string>
+
 #include "base/basictypes.h"
 #include "vendor/node/src/node_object_wrap.h"
 
@@ -19,6 +21,9 @@ class Event : public node::ObjectWrap {
   // Create a V8 Event object.
   static v8::Handle<v8::Object> CreateV8Object();
 
+  // Get JSON string of the event.returnValue from a Event object.
+  static std::string GetReturnValue(v8::Handle<v8::Object> event);
+
   // Accessor to return handle_, this follows Google C++ Style.
   v8::Persistent<v8::Object>& handle() { return handle_; }