Make EfficientLength public, as EfficientLengthIterable.

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.
 
 const int _maxAscii = 0x7f;
 const int _maxLatin1 = 0xff;
 const int _maxUtf16 = 0xffff;
 const int _maxUnicode = 0x10ffff;
 
 patch class String {
@@ skipping 139 matching lines @@
       int code = charCodes[i];
       if (code is! _Smi) throw new ArgumentError(charCodes);
       bits |= code;
     }
     return bits;
   }
 
   static String _createStringFromIterable(Iterable<int> charCodes,
                                           int start, int end) {
     // Treat charCodes as Iterable.
-    if (charCodes is EfficientLength) {
+    if (charCodes is EfficientLengthIterable) {
       int length = charCodes.length;
       end = RangeError.checkValidRange(start, end, length);
       List charCodeList = new List.from(charCodes.take(end).skip(start),
                                         growable: false);
       return createFromCharCodes(charCodeList, 0, charCodeList.length, null);
     }
     // Don't know length of iterable, so iterate and see if all the values
     // are there.
     if (start < 0) throw new RangeError.range(start, 0, charCodes.length);
     var it = charCodes.iterator;
@@ skipping 1143 matching lines @@
     for (int g in groups) {
       result.add(group(g));
     }
     return result;
   }
 
   final int start;
   final String input;
   final String pattern;
 }