[Extensions] Make Event::restrict_to_browser_context const.

chrome/browser/extensions/api/history/history_api.cc

Index: chrome/browser/extensions/api/history/history_api.cc
diff --git a/chrome/browser/extensions/api/history/history_api.cc b/chrome/browser/extensions/api/history/history_api.cc
index a10c6f69f64c2906fda29a4a84f7b1d5ad120c60..b5e49a22470cb2a1d82277d3751269a0d0f433e9 100644
--- a/chrome/browser/extensions/api/history/history_api.cc
+++ b/chrome/browser/extensions/api/history/history_api.cc
@@ -173,9 +173,8 @@ void HistoryEventRouter::DispatchEvent(
     const std::string& event_name,
     std::unique_ptr<base::ListValue> event_args) {
   if (profile && EventRouter::Get(profile)) {
-    std::unique_ptr<Event> event(
-        new Event(histogram_value, event_name, std::move(event_args)));
-    event->restrict_to_browser_context = profile;
+    auto event = base::MakeUnique<Event>(histogram_value, event_name,
+                                         std::move(event_args), profile);
     EventRouter::Get(profile)->BroadcastEvent(std::move(event));
   }
 }