Use a direct include of strings headers in ui/, part 2.

ui/oak/oak_pretty_print.h

 // 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.
 
 #ifndef UI_OAK_OAK_PRETTY_PRINT_H_
 #define UI_OAK_OAK_PRETTY_PRINT_H_
 
-#include "base/string16.h"
+#include "base/strings/string16.h"
 
 namespace gfx {
 class Insets;
 class Rect;
 }
 
 namespace oak {
 namespace internal {
 
 // Functions that return a string consisting of a prefix and the supplied value
 // converted to a pretty string representation.
 base::string16 PropertyWithInteger(const std::string& prefix, int value);
 base::string16 PropertyWithVoidStar(const std::string& prefix, void* ptr);
 base::string16 PropertyWithBool(const std::string& prefix, bool value);
 base::string16 PropertyWithBounds(const std::string& prefix,
                                   const gfx::Rect& bounds);
 base::string16 PropertyWithInsets(const std::string& prefix,
                                   const gfx::Insets& insets);
 
 }  // namespace internal
 }  // namespace oak
 
 #endif  // UI_OAK_OAK_PRETTY_PRINT_H_