Moving ListBase, FixedLengthListMixin and UmodifiableListMixin to collection.

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);
   }
 }
 
@@ skipping 399 matching lines @@
       if (startIndex == endIndex && endIndex == previousIndex) {
         ++startIndex;  // empty match, advance and restart
         continue;
       }
       result.add(this._substringUnchecked(previousIndex, match.start));
       startIndex = previousIndex = endIndex;
     }
     return result;
   }
 
-  List<int> get codeUnits => new CodeUnits(this);
+  List<int> get codeUnits => new _CodeUnits(this);
 
   Runes get runes => new Runes(this);
 
   String toUpperCase() native "String_toUpperCase";
 
   String toLowerCase() native "String_toLowerCase";
 
   // Implementations of Strings methods follow below.
   static String join(Iterable<String> strings, String separator) {
     bool first = true;
@@ skipping 175 matching lines @@
     for (int g in groups) {
       result.add(group(g));
     }
     return result;
   }
 
   final int start;
   final String str;
   final String pattern;
 }
+
+/**
+ * An [Iterable] of the UTF-16 code units of a [String] in index order.
+ */
+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);
+}