List printers managed by extensions in print preview

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<linked_ptr<core_api::printer_provider::PrinterInfo>>;
+
   // Used by chrome.printerProviderInternal API to report
   // chrome.printerProvider.onGetPrintersRequested result returned by the
   // extension |extension|.
   // |request_id| is the request id passed to the original
   // chrome.printerProvider.onGetPrintersRequested event.
   virtual void OnGetPrintersResult(const Extension* extension,
                                    int request_id,
-                                   const base::ListValue& result) = 0;
+                                   const PrinterInfoVector& result) = 0;
 
   // Used by chrome.printerProviderInternal API to report
   // chrome.printerProvider.onGetCapabilityRequested result returned by the
   // extension |extensiod|.
   // |request_id| is the request id passed to the original
   // chrome.printerProvider.onGetCapabilityRequested event.
   virtual void OnGetCapabilityResult(const Extension* extension,
                                      int request_id,
                                      const base::DictionaryValue& result) = 0;
 
   // Used by chrome.printerProviderInternal API to report
   // chrome.printerProvider.onPrintRequested result returned by the extension
   // |extension|.
   // |request_id| is the request id passed to the original
   // chrome.printerProvider.onPrintRequested event.
   virtual void OnPrintResult(
       const Extension* extension,
       int request_id,
       core_api::printer_provider_internal::PrintError error) = 0;
 
  protected:
   virtual ~PrinterProviderInternalAPIObserver() {}
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_API_PRINTER_PROVIDER_INTERNAL_PRINTER_PROVIDER_INTERNAL_API_OBSERVER_H_