PPAPI: Make blocking completion callbacks work.

ppapi/thunk/ppb_layer_compositor_api.h

Index: ppapi/thunk/ppb_layer_compositor_api.h
diff --git a/ppapi/thunk/ppb_layer_compositor_api.h b/ppapi/thunk/ppb_layer_compositor_api.h
index 8d727608b4a149542d5c825d9fc5c23e2baca8a1..883334f982159c5468955aecac3a46a061c39128 100644
--- a/ppapi/thunk/ppb_layer_compositor_api.h
+++ b/ppapi/thunk/ppb_layer_compositor_api.h
@@ -1,13 +1,17 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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_THUNK_PPB_LAYER_COMPOSITOR_API_H_
 #define PPAPI_THUNK_PPB_LAYER_COMPOSITOR_API_H_
 
+#include "base/memory/ref_counted.h"
 #include "ppapi/c/dev/ppb_layer_compositor_dev.h"
 
 namespace ppapi {
+
+class TrackedCallback;
+
 namespace thunk {
 
 class PPB_LayerCompositor_API {
@@ -20,7 +24,7 @@ class PPB_LayerCompositor_API {
   virtual void SetRect(PP_Resource layer, const PP_Rect* rect) = 0;
   virtual void SetDisplay(PP_Resource layer, PP_Bool is_displayed) = 0;
   virtual void MarkAsDirty(PP_Resource layer) = 0;
-  virtual int32_t SwapBuffers(PP_CompletionCallback callback) = 0;
+  virtual int32_t SwapBuffers(scoped_refptr<TrackedCallback> callback) = 0;
 };
 
 }  // namespace thunk