Remove implicit conversions from scoped_refptr to T* in ppapi/

ppapi/shared_impl/tracked_callback.cc

Index: ppapi/shared_impl/tracked_callback.cc
diff --git a/ppapi/shared_impl/tracked_callback.cc b/ppapi/shared_impl/tracked_callback.cc
index 70565a19d1974cff60de56b734d7e7a1549b8a92..7ddfd39c13cb9b2edc626146d64e98238c97f6e9 100644
--- a/ppapi/shared_impl/tracked_callback.cc
+++ b/ppapi/shared_impl/tracked_callback.cc
@@ -167,7 +167,7 @@ void TrackedCallback::PostRun(int32_t result) {
   } else {
     base::Closure callback_closure(
         RunWhileLocked(base::Bind(&TrackedCallback::Run, this, result)));
-    if (target_loop_) {
+    if (target_loop_.get()) {
       target_loop_->PostClosure(FROM_HERE, callback_closure, 0);
     } else {
       // We must be running in-process and on the main thread (the Enter