Mojo C++ bindings: allow StructTraits to return handle or interface types as value.

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 83 matching lines @@
 
 template <>
 struct StructTraits<test::PassByValueStructWithTraits,
                     test::PassByValueStructWithTraitsImpl> {
   // Deserialization to test::PassByValueStructTraitsImpl.
   static bool Read(test::PassByValueStructWithTraits::DataView data,
                    test::PassByValueStructWithTraitsImpl* out);
 
   // Fields in test::PassByValueStructWithTraits.
   // See src/mojo/public/interfaces/bindings/tests/struct_with_traits.mojom.
-  static ScopedHandle& f_handle(test::PassByValueStructWithTraitsImpl& value) {
-    return value.get_mutable_handle();
+  static ScopedHandle f_handle(test::PassByValueStructWithTraitsImpl& value) {
+    return std::move(value.get_mutable_handle());

[Peng, 2016/07/06 18:05:26]

Yes. This is what I need.

   }
 };
 
 template <>
 struct StructTraits<test::StructWithTraitsForUniquePtrTest,
                     std::unique_ptr<int>> {
   static int f_int32(const std::unique_ptr<int>& data) { return *data; }
 
   static bool Read(test::StructWithTraitsForUniquePtrTest::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_