DO NOT SUBMIT. Implement an XPCService for notifications.

chrome/browser/ui/cocoa/notifications/xpc_service_main.mm

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import <AppKit/AppKit.h>
+#import <Foundation/Foundation.h>
+
+#include "base/mac/scoped_nsobject.h"
+#import "chrome/browser/ui/cocoa/notifications/notification_service_delegate.h"
+
+// The main method of the notification alert xpc service.
+// It is initiaized by Chrome on demand whenever a notification of type alert
+// needs to be displayed.
+// The connection will then remain open in order to receive notification
+// clicks and so until all notifications of type alert are closed.
+int main(int argc, const char* argv[]) {
+  @autoreleasepool {
+    base::scoped_nsobject<ServiceDelegate> delegate(
+        [[ServiceDelegate alloc] init]);
+
+    NSXPCListener* listener = [NSXPCListener serviceListener];
+    listener.delegate = delegate.get();
+
+    // Keep the connection open forever since there is no xpc_transaction_end()
+    // TODO(miguelg): send xpc_transaction_end when no alerts are being
+    // displayed.
+    xpc_transaction_begin();
+
+    [listener resume];
+
+    return 0;
+  }
+}