PPAPI: Make blocking completion callbacks work.

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 88d3763a36948b8c9332046c2b4aa1165d3714fc..b1c73b61ffabbb2d32b2d4427663294efc6c59c5 100644
--- a/ppapi/proxy/plugin_dispatcher.h
+++ b/ppapi/proxy/plugin_dispatcher.h
@@ -10,6 +10,7 @@
 
 #include "base/basictypes.h"
 #include "base/hash_tables.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/process.h"
@@ -21,6 +22,7 @@
 #include "ppapi/shared_impl/function_group_base.h"
 #include "ppapi/shared_impl/ppapi_preferences.h"
 #include "ppapi/shared_impl/ppb_view_shared.h"
+#include "ppapi/shared_impl/tracked_callback.h"
 
 namespace ppapi {
 
@@ -38,8 +40,8 @@ struct InstanceData {
 
   PP_Bool flash_fullscreen;  // Used for PPB_FlashFullscreen.
 
-  // When non-0, indicates the callback to execute when mouse lock is lost.
-  PP_CompletionCallback mouse_lock_callback;
+  // When non-NULL, indicates the callback to execute when mouse lock is lost.
+  scoped_refptr<TrackedCallback> mouse_lock_callback;
 };
 
 class PPAPI_PROXY_EXPORT PluginDispatcher