Fix implicit access to raw pointer of scoped_refptr.

mojo/edk/system/shared_buffer_dispatcher.cc

Index: mojo/edk/system/shared_buffer_dispatcher.cc
diff --git a/mojo/edk/system/shared_buffer_dispatcher.cc b/mojo/edk/system/shared_buffer_dispatcher.cc
index f38e2abf1410a55a313c85e0b62ade865c4c6e82..df391050a2ac2ccda65fcc1b58d3d9c07e1aa869 100644
--- a/mojo/edk/system/shared_buffer_dispatcher.cc
+++ b/mojo/edk/system/shared_buffer_dispatcher.cc
@@ -276,7 +276,7 @@ bool SharedBufferDispatcher::BeginTransit() {
   base::AutoLock lock(lock_);
   if (in_transit_)
     return false;
-  in_transit_ = shared_buffer_ != nullptr;
+  in_transit_ = static_cast<bool>(shared_buffer_);
   return in_transit_;
 }