Fix some bad documentation links.

sdk/lib/core/symbol.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.
 
 part of dart.core;
 
 /// Opaque name used by mirrors, invocations and [Function.apply].
 abstract class Symbol {
   /**
    * Constructs a new Symbol.
@@ skipping 13 matching lines @@
    *   "`^`", "`~`", "`<<`", "`>>`", "`<`", "`<=`", "`>`", "`>=`", "`==`",
    *   "`[]`", "`[]=`", or "`unary-`"),
    * * any of the above preceded by any number of qualifiers,
    *   where a qualifier is a non-private identifier followed by '`.`',
    * * or the empty string (the default name of a library with no library
    *   name declaration).
    *
    * The following text is non-normative:
    *
    * Creating non-const Symbol instances may result in larger output.  If
-   * possible, use [MirrorsUsed] in "dart:mirrors" to specify which names might
-   * be passed to this constructor.
+   * possible, use `MirrorsUsed` from "dart:mirrors" to specify which names
+   * might be passed to this constructor.
    */
   const factory Symbol(String name) = internal.Symbol;
 
   /**
    * Returns a hash code compatible with [operator==].
    *
    * Equal symbols have the same hash code.
    */
   int get hashCode;
 
   /**
    * Symbols are equal to other symbols that correspond to the same member name.
    *
    * Qualified member names, like `#foo.bar` are equal only if they have the
    * same identifiers before the same final member name.
    */
   bool operator ==(other);
 }