message: generate addedtypes for event maps
diff: @@ -1278,6 +1278,13 @@ module Emit =
  getEventTypeInInterface eHandler.EventName i
  Pt.Printl "\"%s\": %s;" eHandler.EventName eventType
  + let emitJsonProperty (p: InputJsonType.Root) =
  + let readOnlyModifier =
  + match p.Readonly with
  + | Some(true) -> "readonly "
  + | _ -> ""
  + Pt.Printl "%s%s: %s;" readOnlyModifier p.Name.Value p.Type.Value
  +
  let ownEventHandles = if iNameToEhList.ContainsKey i.Name && not iNameToEhList.[i.Name].IsEmpty then iNameToEhList.[i.Name] else []
  if ownEventHandles.Length > 0 then
  Pt.Printl "interface %sEventMap" i.Name
  @@ -1287,6 +1294,13 @@ module Emit =
  Pt.Print " {"
  Pt.IncreaseIndent()
  ownEventHandles |> List.iter emitInterfaceEventMapEntry
  +
  + let addedProps =
  + getAddedItems ItemKind.Property Flavor.Web
  + |> Array.filter (fun m -> m.Interface.IsNone || m.Interface.Value = i.Name + "EventMap")
  +
  + Array.iter emitJsonProperty addedProps
  +
  Pt.DecreaseIndent()
  Pt.Printl "}"
  Pt.Printl ""
  