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 1080 matching lines @@
    */
   bool get isOptional;
 
   /**
    * Returns [:true:] if the reflectee is a named parameter.
    * Otherwise returns [:false:].
    */
   bool get isNamed;
 
   /**
-   * Returns [:true:] if the reflectee has a default value.
+   * Returns [:true:] if the reflectee has explicitly declared a default value.
    * Otherwise returns [:false:].
    */
   bool get hasDefaultValue;
 
   /**
-   * A mirror on the default value for this parameter, if it exists.
+   * If this is a required parameter, returns [:null:]. Otherwise returns a
+   * mirror on the default value for this parameter. If no default is declared
+   * for an optional parameter, the default is [:null:] and a mirror on [:null:]
+   * is returned.
    */
-  // 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});
 }