Use a direct include of strings headers in ui/, part 1.

ui/app_list/signin_delegate.h

 // Copyright 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 UI_APP_LIST_SIGNIN_DELEGATE_H_
 #define UI_APP_LIST_SIGNIN_DELEGATE_H_
 
 #include "base/basictypes.h"
 #include "base/observer_list.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "ui/app_list/app_list_export.h"
 
 namespace app_list {
 
 class SigninDelegateObserver;
 
 class APP_LIST_EXPORT SigninDelegate {
  public:
   SigninDelegate();
   virtual ~SigninDelegate();
@@ skipping 17 matching lines @@
 
  private:
   ObserverList<SigninDelegateObserver, true> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(SigninDelegate);
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_SIGNIN_DELEGATE_H_