Use a direct include of strings headers in ui/, part 3.

ui/views/corewm/tooltip_controller_test_helper.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 UI_VIEWS_COREWM_TOOLTIP_CONTROLLER_TEST_HELPER_H_
 #define UI_VIEWS_COREWM_TOOLTIP_CONTROLLER_TEST_HELPER_H_
 
 #include "base/logging.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "ui/views/view.h"
 #include "ui/views/views_export.h"
 
 namespace aura {
 class Window;
 }
 
 namespace views {
 namespace corewm {
 
@@ skipping 46 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(TooltipTestView);
 };
 
 
 }  // namespace test
 }  // namespace corewm
 }  // namespace views
 
 #endif  // UI_VIEWS_COREWM_TOOLTIP_CONTROLLER_TEST_HELPER_H_