Compile time error if name is used before variable is declared

runtime/lib/string_patch.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.
 
 patch class String {
   /* patch */ factory String.fromCharCodes(Iterable<int> charCodes) {
     return _StringBase.createFromCharCodes(charCodes);
   }
 
   /* patch */ const factory String.fromEnvironment(String name,
@@ skipping 450 matching lines @@
     for (int i = 0; i < this.length; i++) {
       if (string.codeUnitAt(start + i) != this.codeUnitAt(i)) {
         return null;
       }
     }
     return new _StringMatch(start, string, this);
   }
 
   List<String> split(Pattern pattern) {
     if ((pattern is String) && pattern.isEmpty) {
-      List<String> result = new List<String>(length);
-      for (int i = 0; i < length; i++) {
+      List<String> result = new List<String>(this.length);
+      for (int i = 0; i < this.length; i++) {
         result[i] = this[i];
       }
       return result;
     }
     int length = this.length;
     Iterator iterator = pattern.allMatches(this).iterator;
     if (length == 0 && iterator.moveNext()) {
       // A matched empty string input returns the empty list.
       return <String>[];
     }
@@ skipping 218 matching lines @@
 class _CodeUnits extends Object with ListMixin<int>,
                                      UnmodifiableListMixin<int> {
   /** The string that this is the code units of. */
   String _string;
 
   _CodeUnits(this._string);
 
   int get length => _string.length;
   int operator[](int i) => _string.codeUnitAt(i);
 }