Address Ivan's comments.

sdk/lib/utf/utf16.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.
 
 
 /**
  * Decodes the UTF-16 bytes as an iterable. Thus, the consumer can only convert
  * as much of the input as needed. Determines the byte order from the BOM,
  * or uses big-endian as a default. This method always strips a leading BOM.
  * Set the [replacementCodepoint] to null to throw an ArgumentError
@@ skipping 197 matching lines @@
   }
 }
 
 typedef _ListRangeIterator _CodeUnitsProvider();
 
 /**
  * Return type of [decodeUtf16AsIterable] and variants. The Iterable type
  * provides an iterator on demand and the iterator will only translate bytes
  * as requested by the user of the iterator. (Note: results are not cached.)
  */
+// TODO(floitsch): Consider removing the extend and switch to implements since
+// that's cheaper to allocate.
 class IterableUtf16Decoder extends Iterable<int> {
   final _CodeUnitsProvider codeunitsProvider;
   final int replacementCodepoint;
 
   IterableUtf16Decoder._(this.codeunitsProvider, this.replacementCodepoint);
 
   Utf16CodeUnitDecoder get iterator =>
       new Utf16CodeUnitDecoder.fromListRangeIterator(codeunitsProvider(),
           replacementCodepoint);
 }
@@ skipping 125 matching lines @@
   }
 
   int decode() {
     utf16EncodedBytesIterator.moveNext();
     int lo = utf16EncodedBytesIterator.current;
     utf16EncodedBytesIterator.moveNext();
     int hi = utf16EncodedBytesIterator.current;
     return (hi << 8) + lo;
   }
 }