PPAPI: Make blocking completion callbacks work.

ppapi/thunk/ppb_graphics_3d_api.h

Index: ppapi/thunk/ppb_graphics_3d_api.h
diff --git a/ppapi/thunk/ppb_graphics_3d_api.h b/ppapi/thunk/ppb_graphics_3d_api.h
index 84dc829acdf9b4382e77a389949df460d1957c79..76197b135c5204a145171f978252a02974f21661 100644
--- a/ppapi/thunk/ppb_graphics_3d_api.h
+++ b/ppapi/thunk/ppb_graphics_3d_api.h
@@ -5,12 +5,16 @@
 #ifndef PPAPI_THUNK_PPB_GRAPHICS_3D_API_H_
 #define PPAPI_THUNK_PPB_GRAPHICS_3D_API_H_
 
+#include "base/memory/ref_counted.h"
 #include "ppapi/c/ppb_graphics_3d.h"
 #include "ppapi/c/trusted/ppb_graphics_3d_trusted.h"
 #include "ppapi/c/dev/ppb_gles_chromium_texture_mapping_dev.h"
 #include "ppapi/thunk/ppapi_thunk_export.h"
 
 namespace ppapi {
+
+class TrackedCallback;
+
 namespace thunk {
 
 class PPAPI_THUNK_EXPORT PPB_Graphics3D_API {
@@ -22,7 +26,7 @@ class PPAPI_THUNK_EXPORT PPB_Graphics3D_API {
   virtual int32_t SetAttribs(const int32_t attrib_list[]) = 0;
   virtual int32_t GetError() = 0;
   virtual int32_t ResizeBuffers(int32_t width, int32_t height) = 0;
-  virtual int32_t SwapBuffers(PP_CompletionCallback callback) = 0;
+  virtual int32_t SwapBuffers(scoped_refptr<TrackedCallback> callback) = 0;
 
   // Graphics3DTrusted API.
   virtual PP_Bool InitCommandBuffer() = 0;