Eliminate implicit conversion from scoped_refptr<T> to T*

ppapi/shared_impl/ppapi_globals.h

Index: ppapi/shared_impl/ppapi_globals.h
diff --git a/ppapi/shared_impl/ppapi_globals.h b/ppapi/shared_impl/ppapi_globals.h
index 737c3a287fd3d12e4eb52c171222ed0b5ba6b788..44b9a39ed9005e1d25e6bceab2ce2285f68bd1f6 100644
--- a/ppapi/shared_impl/ppapi_globals.h
+++ b/ppapi/shared_impl/ppapi_globals.h
@@ -6,6 +6,7 @@
 #define PPAPI_SHARED_IMPL_PPAPI_GLOBALS_H_
 
 #include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
 #include "base/threading/thread_local.h"  // For testing purposes only.
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/c/pp_module.h"
@@ -60,7 +61,7 @@ class PPAPI_SHARED_EXPORT PpapiGlobals {
   // Retrieves the corresponding tracker.
   virtual ResourceTracker* GetResourceTracker() = 0;
   virtual VarTracker* GetVarTracker() = 0;
-  virtual CallbackTracker* GetCallbackTrackerForInstance(
+  virtual scoped_refptr<CallbackTracker> GetCallbackTrackerForInstance(
       PP_Instance instance) = 0;
   virtual base::Lock* GetProxyLock() = 0;