Allow Mojo structs as map keys

mojo/public/cpp/bindings/map_traits_stl.h

Index: mojo/public/cpp/bindings/map_traits_stl.h
diff --git a/mojo/public/cpp/bindings/map_traits_stl.h b/mojo/public/cpp/bindings/map_traits_stl.h
index ff79a200d3e87bbf229f92206930db6af8c62bd9..83a4399ce064597cb3062ffa94303d5a0d5af6c1 100644
--- a/mojo/public/cpp/bindings/map_traits_stl.h
+++ b/mojo/public/cpp/bindings/map_traits_stl.h
@@ -94,14 +94,10 @@ struct MapTraits<std::unordered_map<K, V>> {
   static V& GetValue(Iterator& iterator) { return iterator->second; }
   static const V& GetValue(ConstIterator& iterator) { return iterator->second; }
 
-  static bool Insert(std::unordered_map<K, V>& input, const K& key, V&& value) {
-    input.insert(std::make_pair(key, std::forward<V>(value)));
-    return true;
-  }
-  static bool Insert(std::unordered_map<K, V>& input,
-                     const K& key,
-                     const V& value) {
-    input.insert(std::make_pair(key, value));
+  template <typename IK, typename IV>

[yzshen1, 2016/09/20 23:44:40]

nit: It is not very obvious what IK/IV mean. Please update map_traits.h and
comment about these types.

[tibell, 2016/09/21 07:10:53]

Done.

+  static bool Insert(std::unordered_map<K, V>& input, IK&& key, IV&& value) {
+    input.insert(
+        std::make_pair(std::forward<IK>(key), std::forward<IV>(value)));
     return true;
   }