extensions: Cleanup class/struct fwd declarations

extensions/browser/api/printer_provider_internal/printer_provider_internal_api_observer.h

 // Copyright 2015 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 EXTENSIONS_BROWSER_API_PRINTER_PROVIDER_INTERNAL_PRINTER_PROVIDER_INTERNAL_API_OBSERVER_H_
 #define EXTENSIONS_BROWSER_API_PRINTER_PROVIDER_INTERNAL_PRINTER_PROVIDER_INTERNAL_API_OBSERVER_H_
 
 #include <vector>
 
 #include "extensions/common/api/printer_provider.h"
 #include "extensions/common/api/printer_provider_internal.h"
 
 namespace base {
 class DictionaryValue;
-class ListValue;
 }
 
 namespace extensions {
 
 class Extension;
 
 // Interface for observing chrome.printerProviderInternal API function calls.
 class PrinterProviderInternalAPIObserver {
  public:
   using PrinterInfoVector = std::vector<api::printer_provider::PrinterInfo>;
@@ skipping 36 matching lines @@
       int request_id,
       const api::printer_provider::PrinterInfo* printer_info) = 0;
 
  protected:
   virtual ~PrinterProviderInternalAPIObserver() {}
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_API_PRINTER_PROVIDER_INTERNAL_PRINTER_PROVIDER_INTERNAL_API_OBSERVER_H_