Mojo C++ bindings: custom type mapping of map

mojo/public/cpp/bindings/map_traits.h

Index: mojo/public/cpp/bindings/map_traits.h
diff --git a/mojo/public/cpp/bindings/map_traits.h b/mojo/public/cpp/bindings/map_traits.h
new file mode 100644
index 0000000000000000000000000000000000000000..7aa1cbf5507cfe5a521c2e922421508ae65ada4a
--- /dev/null
+++ b/mojo/public/cpp/bindings/map_traits.h
@@ -0,0 +1,54 @@
+// 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
+// a mojom map.
+//
+// Usually you would like to do a partial specialization for a map template.
+// Imagine you want to specialize it for CustomMap<>, you need to implement:
+//
+//   template <typename K, typename V>
+//   struct MapTraits<CustomMap<K, V>> {
+//     using Key = K;
+//     using Value = V;
+//
+//     // These two methods are optional. Please see comments in struct_traits.h
+//     static bool IsNull(const CustomMap<K, V>& input);
+//     static void SetToNull(CustomMap<K, V>* output);
+//
+//     static size_t GetSize(const CustomMap<K, V>& input);
+//
+//     static CustomConstIterator GetBegin(const CustomMap<K, V>& input);
+//     static CustomIterator GetBegin(CustomMap<K, V>& input);
+//
+//     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);
+//
+//     static void Insert(CustomMap<K, V>& input,
+//                        const K& key,
+//                        V&& value);
+//     static void Insert(CustomMap<K, V>& input,
+//                        const K& key,
+//                        const V& value);
+//
+//     static void SetToEmpty(CustomMap<K, V>* output);
+//   };
+//
+template <typename T>
+struct MapTraits;
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_MAP_TRAITS_H_