WIP [esnext] implement async iteration proposal

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 26a3dae1c646632481657f937a30e867672ecbc6..b50734f10b895b48614b70abf8870d2a14d7bb58 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -3942,12 +3942,21 @@ void MacroAssembler::AssertBoundFunction(Register object) {
 
 void MacroAssembler::AssertGeneratorObject(Register object) {
   if (emit_debug_code()) {
+    Label ok;
     testb(object, Immediate(kSmiTagMask));
     Check(not_equal, kOperandIsASmiAndNotAGeneratorObject);
+
     Push(object);
     CmpObjectType(object, JS_GENERATOR_OBJECT_TYPE, object);
     Pop(object);
+    j(equal, &ok, Label::kNear);
+
+    Push(object);
+    CmpObjectType(object, JS_ASYNC_GENERATOR_OBJECT_TYPE, object);
+    Pop(object);
     Check(equal, kOperandIsNotAGeneratorObject);
+
+    bind(&ok);
   }
 }