Implement correct scoping rules for variables.

sdk/lib/collection/list.dart

Index: sdk/lib/collection/list.dart
diff --git a/sdk/lib/collection/list.dart b/sdk/lib/collection/list.dart
index 0e0c6116445554ade256019919d6f97b991f0044..734e63c14afa67ecdf10dbf278a67da465b57e83 100644
--- a/sdk/lib/collection/list.dart
+++ b/sdk/lib/collection/list.dart
@@ -315,7 +315,7 @@ abstract class ListMixin<E> implements List<E> {
   }
 
   List<E> sublist(int start, [int end]) {
-    if (end == null) end = length;
+    if (end == null) end = this.length;
     _rangeCheck(start, end);
     int length = end - start;
     List<E> result = new List<E>()..length = length;