Cleanup: Pass std::string as const reference from ash/ + minor coding style changes in base/

ash/test/test_session_state_delegate.h

 // Copyright (c) 2013 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.
 
 #ifndef ASH_TEST_TEST_SESSION_STATE_DELEGATE_H_
 #define ASH_TEST_TEST_SESSION_STATE_DELEGATE_H_
 
 #include <vector>
 
 #include "ash/session/session_state_delegate.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/gfx/image/image_skia.h"
 
 namespace ash {
 namespace test {
 
 class MockUserInfo;
 
 class TestSessionStateDelegate : public SessionStateDelegate {
  public:
   TestSessionStateDelegate();
   ~TestSessionStateDelegate() override;
 
   void set_logged_in_users(int users) { logged_in_users_ = users; }
   void set_session_state(SessionState session_state) {
     session_state_ = session_state;
   }
-  void AddUser(const std::string user_id);
+  void AddUser(const std::string& user_id);
   const user_manager::UserInfo* GetActiveUserInfo() const;
 
   // SessionStateDelegate:
   content::BrowserContext* GetBrowserContextByIndex(
       MultiProfileIndex index) override;
   content::BrowserContext* GetBrowserContextForWindow(
       aura::Window* window) override;
   content::BrowserContext* GetUserPresentingBrowserContextForWindow(
       aura::Window* window) override;
   int GetMaximumNumberOfLoggedInUsers() const override;
@@ skipping 77 matching lines @@
   // before the profile and browser UI are available.
   SessionState session_state_;
 
   DISALLOW_COPY_AND_ASSIGN(TestSessionStateDelegate);
 };
 
 }  // namespace test
 }  // namespace ash
 
 #endif  // ASH_TEST_TEST_SESSION_STATE_DELEGATE_H_