Mojo C++ bindings: support mapping T and T? differently.

mojo/public/cpp/bindings/tests/struct_with_traits_impl_traits.h

 // Copyright 2016 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_TESTS_STRUCT_WITH_TRAITS_IMPL_TRAITS_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_TESTS_STRUCT_WITH_TRAITS_IMPL_TRAITS_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 106 matching lines @@
                    test::MoveOnlyStructWithTraitsImpl* out);
 
   // Fields in test::MoveOnlyStructWithTraits.
   // See src/mojo/public/interfaces/bindings/tests/struct_with_traits.mojom.
   static ScopedHandle f_handle(test::MoveOnlyStructWithTraitsImpl& value) {
     return std::move(value.get_mutable_handle());
   }
 };
 
 template <>
-struct StructTraits<test::StructWithTraitsForUniquePtrTest,
-                    std::unique_ptr<int>> {
+struct StructTraits<test::StructWithTraitsForUniquePtr, std::unique_ptr<int>> {
+  static bool IsNull(const std::unique_ptr<int>& data) { return !data; }
+  static void SetToNull(std::unique_ptr<int>* data) { data->reset(); }
+
   static int f_int32(const std::unique_ptr<int>& data) { return *data; }
 
-  static bool Read(test::StructWithTraitsForUniquePtrTest::DataView data,
+  static bool Read(test::StructWithTraitsForUniquePtr::DataView data,
                    std::unique_ptr<int>* out) {
     out->reset(new int(data.f_int32()));
     return true;
   }
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_TESTS_STRUCT_WITH_TRAITS_IMPL_TRAITS_H_