Implement ParameterMirror.{isFinal,hasDefaultValue,defaultValue}.

sdk/lib/mirrors/mirrors.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.
 
 // For the purposes of the mirrors library, we adopt a naming
 // convention with respect to getters and setters.  Specifically, for
 // some variable or field...
 //
 //   var myField;
 //
@@ skipping 1077 matching lines @@
 
   /**
    * Returns [:true:] if the reflectee has a default value.
    * Otherwise returns [:false:].
    */
   bool get hasDefaultValue;
 
   /**
    * A mirror on the default value for this parameter, if it exists.
    */
-  // TODO(ahe): This should return an InstanceMirror.
-  String get defaultValue;
+  InstanceMirror get defaultValue;
 }
 
 /**
  * A [SourceLocation] describes the span of an entity in Dart source code.
  */
 abstract class SourceLocation {
 }
 
 /**
  * When an error occurs during the mirrored execution of code, a
@@ skipping 196 matching lines @@
    *
    * When used as metadata on an import of "dart:mirrors", this metadata does
    * not apply to the library in which the annotation is used, but instead
    * applies to the other libraries (all libraries if "*" is used).
    */
   final override;
 
   const MirrorsUsed(
       {this.symbols, this.targets, this.metaTargets, this.override});
 }