WIP [esnext] implement async iteration proposal

src/ast/ast-types.cc

Index: src/ast/ast-types.cc
diff --git a/src/ast/ast-types.cc b/src/ast/ast-types.cc
index 83879215fc3720185b5cd637806f0421b475befc..cda1a5ba9a9b668504464057bada48715801f298 100644
--- a/src/ast/ast-types.cc
+++ b/src/ast/ast-types.cc
@@ -209,6 +209,8 @@ AstType::bitset AstBitsetType::Lub(i::Map* map) {
     case JS_DATE_TYPE:
     case JS_CONTEXT_EXTENSION_OBJECT_TYPE:
     case JS_GENERATOR_OBJECT_TYPE:
+    case JS_ASYNC_GENERATOR_OBJECT_TYPE:
+    case JS_ASYNC_FROM_SYNC_ITERATOR_TYPE:
     case JS_MODULE_NAMESPACE_TYPE:
     case JS_ARRAY_BUFFER_TYPE:
     case JS_ARRAY_TYPE:
@@ -286,6 +288,7 @@ AstType::bitset AstBitsetType::Lub(i::Map* map) {
     case PROPERTY_CELL_TYPE:
     case MODULE_TYPE:
     case MODULE_INFO_ENTRY_TYPE:
+    case ASYNC_GENERATOR_REQUEST_TYPE:
       return kOtherInternal & kTaggedPointer;
 
     // Remaining instance types are unsupported for now. If any of them do