Implement asynchronous interface/plumbing for GetDefaultPrintSettings.

ppapi/proxy/plugin_dispatcher.h

Index: ppapi/proxy/plugin_dispatcher.h
diff --git a/ppapi/proxy/plugin_dispatcher.h b/ppapi/proxy/plugin_dispatcher.h
index d7c118e8df04205d297acf7ad5879652df70f0d8..48c2e31d1448da1b5dfe4d52d2f0d18ce77389e0 100644
--- a/ppapi/proxy/plugin_dispatcher.h
+++ b/ppapi/proxy/plugin_dispatcher.h
@@ -14,6 +14,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/process.h"
 #include "build/build_config.h"
+#include "ppapi/c/dev/pp_print_settings_dev.h"
 #include "ppapi/c/dev/ppb_console_dev.h"
 #include "ppapi/c/pp_rect.h"
 #include "ppapi/c/pp_instance.h"
@@ -47,6 +48,13 @@ struct InstanceData {
 
   // When non-NULL, indicates the callback to execute when mouse lock is lost.
   scoped_refptr<TrackedCallback> mouse_lock_callback;
+
+  // Pointer to the location for the result of |GetDefaultPrintSettings()|.
+  PP_PrintSettings_Dev* default_print_settings;
+
+  // When non-NULL, indicates the callback to execute when the default print
+  // settings are available.
+  scoped_refptr<TrackedCallback> default_print_settings_callback;
 };
 
 class PPAPI_PROXY_EXPORT PluginDispatcher