[Extensions] Make Event::restrict_to_browser_context const.

chrome/browser/extensions/event_router_forwarder.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/extensions/event_router_forwarder.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 114 matching lines @@
     Profile* restrict_to_profile,
     const GURL& event_url) {
 #if defined(OS_CHROMEOS)
   // Extension does not exist for chromeos login.  This needs to be
   // removed once we have an extension service for login screen.
   // crosbug.com/12856.
   if (!extensions::EventRouter::Get(profile))
     return;
 #endif
 
-  std::unique_ptr<Event> event(
-      new Event(histogram_value, event_name, std::move(event_args)));
-  event->restrict_to_browser_context = restrict_to_profile;
+  auto event = base::MakeUnique<Event>(
+      histogram_value, event_name, std::move(event_args), restrict_to_profile);
   event->event_url = event_url;
   if (extension_id.empty()) {
     extensions::EventRouter::Get(profile)->BroadcastEvent(std::move(event));
   } else {
     extensions::EventRouter::Get(profile)
         ->DispatchEventToExtension(extension_id, std::move(event));
   }
 }
 
 }  // namespace extensions