Add mixin accessor.

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 746 matching lines @@
    * null.
    */
   ClassMirror get superclass;
 
   /**
    * A list of mirrors on the superinterfaces of the reflectee.
    */
   List<ClassMirror> get superinterfaces;
 
   /**
+   * The mixin of this class.
+   * If this class is the result of a mixin application of the
+   * form S with M, returns a class mirror on M.
+   * Otherwise returns a class mirror on [reflectee].

[ahe, 2013/10/15 07:00:38]

Otherwise returns this.

[gbracha, 2013/10/15 17:03:21]

That is a stronger specification. In principle, you could return a different
instance of ClassMirror. I deliberately left that open to the implementation.

[ahe, 2013/10/16 07:28:39]

Returning "this" is more accurate in case of subclasses of ClassMirror. This
might be a hypothetical point, as I think all subclasses of ClassMirrors are
going away. It also makes it clear what should happen if you have an original
declaration versus an instantiated type.

However, both these points apply to the class mirror on M as well. But they also
apply to [superclass] and [superinterfaces] above.

Can we somehow clarify this?

+   */
+  ClassMirror get mixin;
+
+  /**
    * An immutable map from names to mirrors for all members of
    * this type.
    *
    * The members of a type are its methods, fields, getters, and
    * setters.  Note that constructors and type variables are not
    * considered to be members of a type.
    *
    * This does not include inherited members.
    */
   Map<Symbol, Mirror> get members;
@@ skipping 599 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});
 }