Use OnceCallback for Mojo binding connection error handlers.

mojo/public/cpp/bindings/lib/connector.cc

Index: mojo/public/cpp/bindings/lib/connector.cc
diff --git a/mojo/public/cpp/bindings/lib/connector.cc b/mojo/public/cpp/bindings/lib/connector.cc
index 9eb458c91b8dcc1f1a3f03828a15e5658737e0c8..46051cb4c6c1ebb554d34a8ba8edaf2555547e34 100644
--- a/mojo/public/cpp/bindings/lib/connector.cc
+++ b/mojo/public/cpp/bindings/lib/connector.cc
@@ -5,7 +5,6 @@
 #include "mojo/public/cpp/bindings/connector.h"
 
 #include <stdint.h>
-#include <utility>
 
 #include "base/bind.h"
 #include "base/lazy_instance.h"
@@ -479,8 +478,8 @@ void Connector::HandleError(bool force_pipe_reset, bool force_async_handler) {
       WaitToReadMore();
   } else {
     error_ = true;
-    if (!connection_error_handler_.is_null())
-      connection_error_handler_.Run();
+    if (connection_error_handler_)
+      std::move(connection_error_handler_).Run();
   }
 }