Implement browser side of PPB_Printing resource.

ppapi/cpp/dev/printing_dev.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 PPAPI_CPP_DEV_PRINTING_DEV_H_
 #define PPAPI_CPP_DEV_PRINTING_DEV_H_
 
 #include "ppapi/c/dev/ppp_printing_dev.h"
+#include "ppapi/cpp/completion_callback.h"
 #include "ppapi/cpp/instance_handle.h"
 #include "ppapi/cpp/resource.h"
 
 namespace pp {
 
 class Instance;
 
 // You would typically use this either via inheritance on your instance or
 // by composition: see find_dev.h for an example.
-class Printing_Dev {
+class Printing_Dev : public Resource {
  public:
   // The instance parameter must outlive this class.
   explicit Printing_Dev(Instance* instance);
   virtual ~Printing_Dev();
 
   // PPP_Printing_Dev functions exposed as virtual functions for you to
   // override.
   virtual uint32_t QuerySupportedPrintOutputFormats() = 0;
   virtual int32_t PrintBegin(const PP_PrintSettings_Dev& print_settings) = 0;
   virtual Resource PrintPages(const PP_PrintPageNumberRange_Dev* page_ranges,
                               uint32_t page_range_count) = 0;
   virtual void PrintEnd() = 0;
   virtual bool IsPrintScalingDisabled() = 0;
 
   // PPB_Printing_Dev functions.
   // Returns true if the browser supports the required PPB_Printing_Dev
   // interface.
   static bool IsAvailable();
 
-  // Outputs the default print settings for the default printer into
-  // |print_settings|. Returns false on error.
-  bool GetDefaultPrintSettings(PP_PrintSettings_Dev* print_settings) const;
+  // Get the default print settings and store them in the output of |callback|.
+  // This method always runs asynchronously and the callback will always be
+  // triggered.
+  void GetDefaultPrintSettings(
+      const CompletionCallbackWithOutput<PP_PrintSettings_Dev>& callback) const;
 
  private:
   InstanceHandle associated_instance_;
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_DEV_PRINTING_DEV_H_