[Extensions] Make Event::restrict_to_browser_context const.

chrome/browser/speech/extension_api/tts_extension_api.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/speech/extension_api/tts_extension_api.h"
 
 #include <stddef.h>
 
 #include <memory>
 #include <string>
@@ skipping 122 matching lines @@
   details->SetString(constants::kEventTypeKey, event_type_string);
   if (event_type == TTS_EVENT_ERROR) {
     details->SetString(constants::kErrorMessageKey, error_message);
   }
   details->SetInteger(constants::kSrcIdKey, utterance->src_id());
   details->SetBoolean(constants::kIsFinalEventKey, utterance->finished());
 
   std::unique_ptr<base::ListValue> arguments(new base::ListValue());
   arguments->Append(std::move(details));
 
-  std::unique_ptr<extensions::Event> event(
-      new extensions::Event(::extensions::events::TTS_ON_EVENT,
-                            ::events::kOnEvent, std::move(arguments)));
-  event->restrict_to_browser_context = utterance->browser_context();
+  auto event = base::MakeUnique<extensions::Event>(
+      ::extensions::events::TTS_ON_EVENT, ::events::kOnEvent,
+      std::move(arguments), utterance->browser_context());
   event->event_url = utterance->src_url();
   extensions::EventRouter::Get(utterance->browser_context())
       ->DispatchEventToExtension(src_extension_id_, std::move(event));
 
   if (utterance->finished())
     delete this;
 }
 
 bool TtsSpeakFunction::RunAsync() {
   std::string text;
@@ skipping 212 matching lines @@
 
 static base::LazyInstance<
     BrowserContextKeyedAPIFactory<TtsAPI>>::DestructorAtExit g_factory =
     LAZY_INSTANCE_INITIALIZER;
 
 BrowserContextKeyedAPIFactory<TtsAPI>* TtsAPI::GetFactoryInstance() {
   return g_factory.Pointer();
 }
 
 }  // namespace extensions