Use OnceCallback for Mojo binding connection error handlers.

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

Index: mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
diff --git a/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc b/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
index ef3a1fe6800fe052d5f8bc15e04bea7c10a1a4fd..6019b4559130248ba7a05094e358dd76bb7b2487 100644
--- a/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
+++ b/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
@@ -6,8 +6,6 @@
 
 #include <stdint.h>
 
-#include <utility>
-
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
@@ -309,16 +307,14 @@ void InterfaceEndpointClient::NotifyError(
 
   control_message_proxy_.OnConnectionError();
 
-  if (!error_handler_.is_null()) {
-    base::Closure error_handler = std::move(error_handler_);
-    error_handler.Run();
-  } else if (!error_with_reason_handler_.is_null()) {
-    ConnectionErrorWithReasonCallback error_with_reason_handler =
-        std::move(error_with_reason_handler_);
+  if (error_handler_) {
+    std::move(error_handler_).Run();
+  } else if (error_with_reason_handler_) {
     if (reason) {
-      error_with_reason_handler.Run(reason->custom_reason, reason->description);
+      std::move(error_with_reason_handler_)
+          .Run(reason->custom_reason, reason->description);
     } else {
-      error_with_reason_handler.Run(0, std::string());
+      std::move(error_with_reason_handler_).Run(0, std::string());
     }
   }
 }