Remove deprecated StringBuffer.add, addAll and addCharCode.

sdk/lib/_internal/compiler/implementation/mirrors/mirrors_util.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.
 
 library mirrors_util;
 
 import 'dart:collection' show Queue;
 
 // TODO(rnystrom): Use "package:" URL (#4968).
 import 'mirrors.dart';
@@ skipping 120 matching lines @@
     return match[1];
   }
   match = _multiLineCommentStartEnd.firstMatch(comment);
   if (match != null) {
     comment = match[1];
     var sb = new StringBuffer();
     List<String> lines = comment.split('\n');
     for (int index = 0 ; index < lines.length ; index++) {
       String line = lines[index];
       if (index == 0) {
-        sb.add(line); // Add the first line unprocessed.
+        sb.write(line); // Add the first line unprocessed.
         continue;
       }
-      sb.add('\n');
+      sb.write('\n');
       match = _multiLineCommentLineStart.firstMatch(line);
       if (match != null) {
-        sb.add(match[1]);
+        sb.write(match[1]);
       } else if (index < lines.length-1 || !line.trim().isEmpty) {
         // Do not add the last line if it only contains white space.
         // This interprets cases like
         //     /*
         //      * Foo
         //      */
         // as "\nFoo\n" and not as "\nFoo\n     ".
-        sb.add(line);
+        sb.write(line);
       }
     }
     return sb.toString();
   }
   throw new ArgumentError('Invalid comment $comment');
 }