Some more removals of dart:utf.

pkg/source_maps/lib/span.dart

 // Copyright (c) 2013, 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.
 
 /// Dart classes representing the souce spans and source files.
 library source_maps.span;
 
-import 'dart:utf' show stringToCodepoints;
 import 'dart:math' show min, max;
 
 import 'src/utils.dart';
 
 /// A simple class that describe a segment of source text.
 abstract class Span implements Comparable {
   /// The start location of this span.
   final Location start;
 
   /// The end location of this span, exclusive.
@@ skipping 175 matching lines @@
 class SourceFile {
   /// Url where the source file is located.
   final String url;
   final List<int> _lineStarts;
   final List<int> _decodedChars;
 
   SourceFile(this.url, this._lineStarts, this._decodedChars);
 
   SourceFile.text(this.url, String text)
       : _lineStarts = <int>[0],
-        _decodedChars = stringToCodepoints(text) {
+        _decodedChars = text.runes.toList() {
     for (int i = 0; i < _decodedChars.length; i++) {
       var c = _decodedChars[i];
       if (c == _CR) {
         // Return not followed by newline is treated as a newline
         int j = i + 1;
         if (j >= _decodedChars.length || _decodedChars[j] != _LF) {
           c = _LF;
         }
       }
       if (c == _LF) _lineStarts.add(i + 1);
@@ skipping 137 matching lines @@
   int getOffset(int line, int column) =>
     super.getOffset(line - _baseLine,
         line == _baseLine ? column - _baseColumn : column) + _baseOffset;
 
   /// Retrieve the text associated with the specified range. This method
   /// operates on the real offsets from the original file, so that error
   /// messages can be reported accurately.
   String getText(int start, [int end]) =>
     super.getText(start - _baseOffset, end == null ? null : end - _baseOffset);
 }