[Extensions] Make Event::restrict_to_browser_context const.

chrome/browser/extensions/api/cookies/cookies_api.cc

Index: chrome/browser/extensions/api/cookies/cookies_api.cc
diff --git a/chrome/browser/extensions/api/cookies/cookies_api.cc b/chrome/browser/extensions/api/cookies/cookies_api.cc
index a8375ad7dde2d077d67a56586cb6ab78f45a36e8..ac15e13c4d305436e0b2f6d08ac2771f81f8b7e2 100644
--- a/chrome/browser/extensions/api/cookies/cookies_api.cc
+++ b/chrome/browser/extensions/api/cookies/cookies_api.cc
@@ -193,9 +193,8 @@ void CookiesEventRouter::DispatchEvent(
   EventRouter* router = context ? EventRouter::Get(context) : NULL;
   if (!router)
     return;
-  std::unique_ptr<Event> event(
-      new Event(histogram_value, event_name, std::move(event_args)));
-  event->restrict_to_browser_context = context;
+  auto event = base::MakeUnique<Event>(histogram_value, event_name,
+                                       std::move(event_args), context);
   event->event_url = cookie_domain;
   router->BroadcastEvent(std::move(event));
 }