Negative numbers should not be >>> shifted.

lib/compiler/implementation/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('native_helper.dart');
@@ skipping 160 matching lines @@
   return UNINTERCEPTED(a << b);
 }
 
 shr(var a, var b) {
   // TODO(floitsch): inputs must be integers.
   if (checkNumbers(a, b)) {
     if (b < 0) throw new IllegalArgumentException(b);
     // JavaScript only looks at the last 5 bits of the shift-amount. Shifting
     // by 33 is hence equivalent to a shift by 1.
     if (b > 31) return 0;
-    return JS('num', @'# >>> #', a, b);
+    if (a >= 0) return JS('num', @'# >>> #', a, b);
+    return JS('num', @'(# >> #) >>> 0', a, b);

[ngeoffray, 2012/05/22 15:46:31]

Please add a comment on what this entails.

[floitsch, 2012/05/22 21:07:37]

Done.

   }
   return UNINTERCEPTED(a >> b);
 }
 
 and(var a, var b) {
   // TODO(floitsch): inputs must be integers.
   if (checkNumbers(a, b)) {
     return JS('num', @'(# & #) >>> 0', a, b);
   }
   return UNINTERCEPTED(a & b);
@@ skipping 711 matching lines @@
   if (JS('bool', '!!#[#]', value, property)) return value;
   propertyTypeError(value, property);
 }
 
 listSuperNativeTypeCheck(value, property) {
   if (value === null) return value;
   if (value is List) return value;
   if (JS('bool', '#[#]()', value, property)) return value;
   propertyTypeError(value, property);
 }