for-of should throw if result object is not an object

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index faccb90457675627e553b42291f40c75b26b9dce..9b86d0b51292f6291b734962af0f8912e8218f4d 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -942,12 +942,12 @@ class ForOfStatement FINAL : public ForEachStatement {
     return subject();
   }
 
-  // var iterator = subject[Symbol.iterator]();
+  // iterator = subject[Symbol.iterator]()
   Expression* assign_iterator() const {
     return assign_iterator_;
   }
 
-  // var result = iterator.next();
+  // result = iterator.next()  // with type check
   Expression* next_result() const {
     return next_result_;
   }