[parser] Fix preparsing of modules containing labels

Fixes spurious DCHECK triggering due to bug introduced in
https://chromium-review.googlesource.com/c/v8/v8/+/1836258.

Bug: chromium:1011596
Change-Id: Ia3b1eb25d326e465b3239f191aad11d90a2e56a8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1844777Reviewed-by: Sathya Gunasekaran  <gsathya@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64125}

src/parsing/preparser.h

@@ -1073,7 +1073,7 @@ class PreParser : public ParserBase<PreParser> {
   V8_INLINE void DeclareLabel(ZonePtrList<const AstRawString>** labels,
                               ZonePtrList<const AstRawString>** own_labels,
                               const AstRawString* label) {
-    DCHECK(!parsing_module_);
+    DCHECK(!parsing_module_ || !label->IsOneByteEqualTo("await"));
   }
 
   // TODO(nikolaos): The preparser currently does not keep track of labels.
@@ -1326,10 +1326,6 @@ class PreParser : public ParserBase<PreParser> {
     return identifier.IsEvalOrArguments();
   }
 
-  V8_INLINE bool IsAwait(const PreParserIdentifier& identifier) const {
-    return identifier.IsAwait();
-  }
-
   // Returns true if the expression is of type "this.foo".
   V8_INLINE static bool IsThisProperty(const PreParserExpression& expression) {
     return expression.IsThisProperty();

test/mjsunit/regress/regress-crbug-1011596-module.mjs

+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+export function foo() {
+  { label: 1 }
+  return 42;
+}

test/mjsunit/regress/regress-crbug-1011596.mjs

+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import "./regress-crbug-1011596-module.mjs"