[parser] Set rewritable_length to the correct length rather than 0

Bug: chromium:908975
Change-Id: I3dd9cf32de5b11554c2e1cbc0538c9b11ecda09d
Reviewed-on: https://chromium-review.googlesource.com/c/1352286Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57892}

src/parsing/parser-base.h

@@ -1745,7 +1745,8 @@ ParserBase<Impl>::ParsePrimaryExpression() {
 
     if (peek() == Token::ARROW) {
       scope_snapshot_ = std::move(Scope::Snapshot(scope()));
-      rewritable_length_ = 0;
+      rewritable_length_ = static_cast<int>(
+          function_state_->destructuring_assignments_to_rewrite().size());
     }
     return impl()->ExpressionFromIdentifier(name, beg_pos, infer);
   }

test/mjsunit/regress/regress-908975.js

+// Copyright 2018 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.
+
+[] = [];
+a => 0