Allow Mojo structs as map keys

mojo/public/cpp/bindings/map_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_MAP_TRAITS_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_MAP_TRAITS_H_
 
 namespace mojo {
 
 // This must be specialized for any type |T| to be serialized/deserialized as
@@ skipping 19 matching lines @@
 //     static void AdvanceIterator(CustomConstIterator& iterator);
 //     static void AdvanceIterator(CustomIterator& iterator);
 //
 //     static const K& GetKey(CustomIterator& iterator);
 //     static const K& GetKey(CustomConstIterator& iterator);
 //
 //     static V& GetValue(CustomIterator& iterator);
 //     static const V& GetValue(CustomConstIterator& iterator);
 //
 //     // Returning false results in deserialization failure and causes the
-//     // message pipe receiving it to be disconnected.
+//     // message pipe receiving it to be disconnected. |IK| and |IV| are
+//     // separate input key/value template parameters that allows for the
+//     // the key/value types to be forwarded.
+//     template <typename IK, typename IV>
 //     static bool Insert(CustomMap<K, V>& input,
-//                        const K& key,
-//                        V&& value);
-//     static bool Insert(CustomMap<K, V>& input,
-//                        const K& key,
-//                        const V& value);
+//                        IK&& key,
+//                        IV&& value);
 //
 //     static void SetToEmpty(CustomMap<K, V>* output);
 //   };
 //
 template <typename T>
 struct MapTraits;
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_MAP_TRAITS_H_