Mojo C++ bindings: custom type mapping of map

mojo/public/cpp/bindings/struct_traits.h

Index: mojo/public/cpp/bindings/struct_traits.h
diff --git a/mojo/public/cpp/bindings/struct_traits.h b/mojo/public/cpp/bindings/struct_traits.h
index 3dfb7f11445556b71c6b792c9530e9cfb94d4ed9..ba83cd94b4db9979da3af9025c0853b21e14a56c 100644
--- a/mojo/public/cpp/bindings/struct_traits.h
+++ b/mojo/public/cpp/bindings/struct_traits.h
@@ -30,6 +30,10 @@ namespace mojo {
 //          Value or reference of any type that has an ArrayTraits defined.
 //          Supported by default: std::vector, WTF::Vector (in blink).
 //
+//        - map:
+//          Value or reference of any type that has a MapTraits defined.
+//          Supported by default: std::map.
+//
 //        - struct:
 //          Value or reference of any type that has a StructTraits defined.
 //