Use a direct include of strings headers in ppapi/, printing/.

printing/printing_context.h

 // Copyright (c) 2011 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 PRINTING_PRINTING_CONTEXT_H_
 #define PRINTING_PRINTING_CONTEXT_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/callback.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "printing/print_settings.h"
 #include "ui/gfx/native_widget_types.h"
 
 namespace base {
 class DictionaryValue;
 }
 
 namespace printing {
 
 // An abstraction of a printer context, implemented by objects that describe the
@@ skipping 104 matching lines @@
 
   // The application locale.
   std::string app_locale_;
 
   DISALLOW_COPY_AND_ASSIGN(PrintingContext);
 };
 
 }  // namespace printing
 
 #endif  // PRINTING_PRINTING_CONTEXT_H_