Convert arguments to V8 directly in EventEmitter::Emmit

This gets rid of the extra conversion between ListValue.

atom/common/native_mate_converters/value_converter.cc

@@ -37,4 +37,10 @@ bool Converter<base::ListValue>::FromV8(v8::Isolate* isolate,
   }
 }
 
+v8::Handle<v8::Value> Converter<base::ListValue>::ToV8(
+    v8::Isolate* isolate,
+    const base::ListValue& val) {
+  return v8::Undefined(isolate);
+}
+
 }  // namespace mate