Remove deprecated string features.

sdk/lib/_internal/compiler/implementation/lib/string_helper.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.
 
 part of _js_helper;
 
 class StringMatch implements Match {
   const StringMatch(int this.start,
                     String this.str,
                     String this.pattern);
@@ skipping 127 matching lines @@
 
 stringReplaceAllEmptyFuncUnchecked(receiver, onMatch, onNonMatch) {
   // Pattern is the empty string.
   StringBuffer buffer = new StringBuffer();
   int length = receiver.length;
   int i = 0;
   buffer.add(onNonMatch(""));
   while (i < length) {
     buffer.add(onMatch(new StringMatch(i, receiver, "")));
     // Special case to avoid splitting a surrogate pair.
-    int code = receiver.charCodeAt(i);
+    int code = receiver.codeUnitAt(i);
     if ((code & ~0x3FF) == 0xD800 && length > i + 1) {
       // Leading surrogate;
-      code = receiver.charCodeAt(i + 1);
+      code = receiver.codeUnitAt(i + 1);
       if ((code & ~0x3FF) == 0xDC00) {
         // Matching trailing surrogate.
         buffer.add(onNonMatch(receiver.substring(i, i + 2)));
         i += 2;
         continue;
       }
     }
     buffer.add(onNonMatch(receiver[i]));
     i++;
   }
@@ skipping 33 matching lines @@
   } else {
     checkNull(from);
     // TODO(floitsch): implement generic String.replace (with patterns).
     throw "String.replace(Pattern) UNIMPLEMENTED";
   }
 }
 
 stringJoinUnchecked(array, separator) {
   return JS('String', r'#.join(#)', array, separator);
 }