Convert function.length to API-style accessor.

test/mjsunit/function-length-accessor.js

+// Copyright 2014 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.
+
+// Flags: --harmony-scoping
+
+function foo(a, b, c, d) {
+  "use strict"
+  const x = 10;
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  // long comment to trigger lazy compilation.
+  x = 20; // This will trigger compile error with harmony scoping.
+}
+
+assertThrows("foo.length()");