Mojo C++ bindings: support attaching context object for StructTraits.

mojo/public/cpp/bindings/lib/serialization_util.h

Index: mojo/public/cpp/bindings/lib/serialization_util.h
diff --git a/mojo/public/cpp/bindings/lib/serialization_util.h b/mojo/public/cpp/bindings/lib/serialization_util.h
index 698e90d96284476a454885e241632da5747d1215..3c9482ce6fb1a29480a70eaba7ac4ffdcb157d7e 100644
--- a/mojo/public/cpp/bindings/lib/serialization_util.h
+++ b/mojo/public/cpp/bindings/lib/serialization_util.h
@@ -213,18 +213,18 @@ struct CustomContextHelper<Traits, false> {
   }
 };
 
-template <typename ReturnType, typename ParamType, typename MaybeConstUserType>
+template <typename ReturnType, typename ParamType, typename InputUserType>
 ReturnType CallWithContext(ReturnType (*f)(ParamType, void*),
-                           MaybeConstUserType& input,
+                           InputUserType&& input,
                            void* context) {
-  return f(input, context);
+  return f(std::forward<InputUserType>(input), context);
 }
 
-template <typename ReturnType, typename ParamType, typename MaybeConstUserType>
+template <typename ReturnType, typename ParamType, typename InputUserType>
 ReturnType CallWithContext(ReturnType (*f)(ParamType),
-                           MaybeConstUserType& input,
+                           InputUserType&& input,
                            void* context) {
-  return f(input);
+  return f(std::forward<InputUserType>(input));
 }
 
 }  // namespace internal