[Extensions] Make Event::restrict_to_browser_context const.

chrome/browser/extensions/event_router_forwarder.cc

Index: chrome/browser/extensions/event_router_forwarder.cc
diff --git a/chrome/browser/extensions/event_router_forwarder.cc b/chrome/browser/extensions/event_router_forwarder.cc
index 91ec456caebb4903038d5867ae6f5db546f3993b..54a742c7bf87a13d6cf4445ce051c981e9fbd675 100644
--- a/chrome/browser/extensions/event_router_forwarder.cc
+++ b/chrome/browser/extensions/event_router_forwarder.cc
@@ -132,9 +132,8 @@ void EventRouterForwarder::CallEventRouter(
     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));