Implement asynchronous interface/plumbing for GetDefaultPrintSettings.

ppapi/api/dev/ppb_printing_dev.idl

 /* 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.
  */
 
 /**
  * Definition of the PPB_Printing interface.
  */
 
 // Note: This version should always match the PPP_Printing_Dev interface.
 label Chrome {
-  M21 = 0.6
+  M21 = 0.6,
+  M23 = 0.7
 };
 
 interface PPB_Printing_Dev {
+  [version=0.6, deprecate=0.7]
+  PP_Bool GetDefaultPrintSettings([in] PP_Instance instance,
+                                  [out] PP_PrintSettings_Dev print_settings);
+
   /**
    * Outputs the default print settings for the default printer into
-   * <code>print_settings</code>. Returns <code>PP_FALSE</code> on error.
+   * <code>print_settings</code>. The completion callback is triggered when
+   * the settings have been copied into <code>print_settings</code>.
+   * <code>PP_ERROR_INPROGRESS</code> is returned if there is an outstanding
+   * request for the print settings in progress.
    */
-  PP_Bool GetDefaultPrintSettings([in] PP_Instance instance,
-                                  [out] PP_PrintSettings_Dev print_settings);
+  [version=0.7]
+  int32_t GetDefaultPrintSettings([in] PP_Instance instance,
+                                  [out] PP_PrintSettings_Dev print_settings,
+                                  [in] PP_CompletionCallback callback);
 };