Mojo C++ bindings: add a new mode to generator to use native STL/WTF types

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 2d5c137ff355d1526a7561d6b64bb6d010309865..ff79a200d3e87bbf229f92206930db6af8c62bd9 100644
--- a/mojo/public/cpp/bindings/map_traits_stl.h
+++ b/mojo/public/cpp/bindings/map_traits_stl.h
@@ -6,6 +6,7 @@
 #define MOJO_PUBLIC_CPP_BINDINGS_MAP_TRAITS_STL_H_
 
 #include <map>
+#include <unordered_map>
 
 #include "mojo/public/cpp/bindings/map_traits.h"
 
@@ -56,6 +57,57 @@ struct MapTraits<std::map<K, V>> {
   static void SetToEmpty(std::map<K, V>* output) { output->clear(); }
 };
 
+template <typename K, typename V>
+struct MapTraits<std::unordered_map<K, V>> {
+  using Key = K;
+  using Value = V;
+  using Iterator = typename std::unordered_map<K, V>::iterator;
+  using ConstIterator = typename std::unordered_map<K, V>::const_iterator;
+
+  static bool IsNull(const std::unordered_map<K, V>& input) {
+    // std::unordered_map<> is always converted to non-null mojom map.
+    return false;
+  }
+
+  static void SetToNull(std::unordered_map<K, V>* output) {
+    // std::unordered_map<> doesn't support null state. Set it to empty instead.
+    output->clear();
+  }
+
+  static size_t GetSize(const std::unordered_map<K, V>& input) {
+    return input.size();
+  }
+
+  static ConstIterator GetBegin(const std::unordered_map<K, V>& input) {
+    return input.begin();
+  }
+  static Iterator GetBegin(std::unordered_map<K, V>& input) {
+    return input.begin();
+  }
+
+  static void AdvanceIterator(ConstIterator& iterator) { iterator++; }
+  static void AdvanceIterator(Iterator& iterator) { iterator++; }
+
+  static const K& GetKey(Iterator& iterator) { return iterator->first; }
+  static const K& GetKey(ConstIterator& iterator) { return iterator->first; }
+
+  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));
+    return true;
+  }
+
+  static void SetToEmpty(std::unordered_map<K, V>* output) { output->clear(); }
+};
+
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_MAP_TRAITS_STL_H_