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

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

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_SERIALIZATION_UTIL_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_SERIALIZATION_UTIL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 195 matching lines @@
   }
 
   static void* GetNext(SerializationContext* context) { return nullptr; }
 
   template <typename MaybeConstUserType>
   static void TearDown(MaybeConstUserType& input, void* custom_context) {
     DCHECK(!custom_context);
   }
 };
 
-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
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_SERIALIZATION_UTIL_H_