Improve return type of markUnmodifiableList to JSArray instead of List.

sdk/lib/internal/list.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart._internal;
 
 /**
  * Mixin that throws on the length changing operations of [List].
  *
  * Intended to mix-in on top of [ListMixin] for fixed-length lists.
@@ skipping 343 matching lines @@
  *
  * For internal use only.
  * Only works on growable lists as created by `[]` or `new List()`.
  * May throw on any other list.
  *
  * The operation is efficient. It doesn't copy the elements, but converts
  * the existing list directly to a fixed length list.
  * That means that it is a destructive conversion.
  * The original list should not be used afterwards.
  *
- * The returned list may be the same list as the orginal,
+ * The returned list may be the same list as the original,
  * or it may be a different list (according to [identical]).
  * The original list may have changed type to be a fixed list,
  * or become empty or been otherwise modified.
  * It will still be a valid object, so references to it will not, e.g., crash
  * the runtime if accessed, but no promises are made wrt. its contents.
  *
  * This unspecified behavior is the reason the function is not exposed to
  * users. We allow the underlying implementation to make the most efficient
  * conversion, at the cost of leaving the original list in an unspecified
  * state.
  */
 external List makeListFixedLength(List growableList);
 
 /**
  * Converts a fixed-length list to an unmodifiable list.
  *
  * For internal use only.
  * Only works for core fixed-length lists as created by `new List(length)`,
  * or as returned by [makeListFixedLength].
  *
  * The operation is efficient. It doesn't copy the elements, but converts
  * the existing list directly to a fixed length list.
  * That means that it is a destructive conversion.
  * The original list should not be used afterwards.
  *
- * The unmodifialbe list type is similar to the one used by const lists.
+ * The unmodifiable list type is similar to the one used by const lists.
  */
 external List makeFixedListUnmodifiable(List fixedLengthList);