Prevent sort on immutable lists.

dart/frog/leg/lib/js_helper.dart

 // Copyright (c) 2012, 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.
 
 #library('js_helper');
 
 #import('coreimpl.dart');
 
 #source('constant_map.dart');
 #source('date_helper.dart');
@@ skipping 766 matching lines @@
   if (!isJsArray(receiver)) {
     return UNINTERCEPTED(receiver.every(f));
   } else {
     return Collections.every(receiver, f);
   }
 }
 
 builtin$sort$1(receiver, compare) {
   if (!isJsArray(receiver)) return UNINTERCEPTED(receiver.sort(compare));
 
+  checkMutable(receiver, 'sort');
   DualPivotQuicksort.sort(receiver, compare);
 }
 
 checkNull(object) {
   if (object === null) throw new NullPointerException();
   return object;
 }
 
 checkNum(value) {
   if (value is !num) {
@@ skipping 559 matching lines @@
 }
 
 /**
  * Represents the type of Null. The compiler treats this specially.
  */
 class Null {
   factory Null() {
     throw UnsupportedOperationException('new Null()');
   }
 }
+
+builtin$copyFrom$4(receiver, arg1, arg2, arg3, arg4) {
+  // TODO(ahe): Remove this method when CL 9839101 has landed.
+  if (!isJsArray(receiver)) {
+    return UNINTERCEPTED(receiver.copyFrom(arg1, arg2, arg3, arg4));
+  }
+  throw new UnsupportedOperationException('copyFrom');
+}