Cleanup: Pass std::string as const reference if possible

chrome/browser/extensions/api/notifications/notifications_apitest.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 "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/extensions/api/notifications/notifications_api.h"
 #include "chrome/browser/extensions/extension_apitest.h"
@@ skipping 79 matching lines @@
         extensions::NOTIFICATION_EXTENSION_BACKGROUND_PAGE_READY,
         content::NotificationService::AllSources());
     const extensions::Extension* extension = LoadExtension(extdir);
     if (extension) {
       page_created.Wait();
     }
     return extension;
   }
 
  protected:
-  std::string GetNotificationIdFromDelegateId(std::string delegate_id) {
+  std::string GetNotificationIdFromDelegateId(const std::string& delegate_id) {
     return g_browser_process->notification_ui_manager()
         ->FindById(
               delegate_id,
               NotificationUIManager::GetProfileID(
                   g_browser_process->profile_manager()->GetLastUsedProfile()))
         ->id();
   }
 };
 
 }  // namespace
@@ skipping 171 matching lines @@
     notification->ButtonClick(0);
     EXPECT_TRUE(catcher.GetNextResult());
     notification->Click();
     EXPECT_TRUE(catcher.GetNextResult());
     notification->Close(true);
     EXPECT_TRUE(catcher.GetNextResult());
     notification->Close(false);
     EXPECT_FALSE(catcher.GetNextResult());
   }
 }