Implement asynchronous interface/plumbing for GetDefaultPrintSettings.

ppapi/api/dev/ppb_printing_dev.idl

Index: ppapi/api/dev/ppb_printing_dev.idl
diff --git a/ppapi/api/dev/ppb_printing_dev.idl b/ppapi/api/dev/ppb_printing_dev.idl
index 5627858525c76ff39c9b50d0e0ad614a699fac88..a58c261c2486d7a103098c0a70c1de3ade9a5d1b 100644
--- a/ppapi/api/dev/ppb_printing_dev.idl
+++ b/ppapi/api/dev/ppb_printing_dev.idl
@@ -9,14 +9,24 @@
 
 // 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);
 };