Cleanup remaining class/struct fwd declarations

printing/printing_context_chromeos.h

 // Copyright 2016 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_CHROMEOS_H_
 #define PRINTING_PRINTING_CONTEXT_CHROMEOS_H_
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "printing/backend/cups_connection.h"
 #include "printing/backend/cups_printer.h"
 #include "printing/printing_context.h"
 
-namespace base {
-class DictionaryValue;
-}
-
 namespace printing {
 
 class PRINTING_EXPORT PrintingContextChromeos : public PrintingContext {
  public:
   explicit PrintingContextChromeos(Delegate* delegate);
   ~PrintingContextChromeos() override;
 
   // PrintingContext implementation.
   void AskUserForSettings(int max_pages,
                           bool has_selection,
@@ skipping 23 matching lines @@
 
   CupsConnection connection_;
   std::unique_ptr<CupsPrinter> printer_;
 
   DISALLOW_COPY_AND_ASSIGN(PrintingContextChromeos);
 };
 
 }  // namespace printing
 
 #endif  // PRINTING_PRINTING_CONTEXT_CHROMEOS_H_