Add ClassMirror.isAbstract to the API and VM implementation.

sdk/lib/mirrors/mirrors.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.
 
 // 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 687 matching lines @@
    * If this type is [:Object:], the superclass will be null.
    */
   ClassMirror get superclass;
 
   /**
    * A list of mirrors on the superinterfaces of the reflectee.
    */
   List<ClassMirror> get superinterfaces;
 
   /**
+   * Is the reflectee abstract?
+   */
+  bool get isAbstract;
+
+  /**
    * Returns an immutable map of the declarations actually given in the class
    * declaration.
    *
    * This map includes all regular methods, getters, setters, fields,
    * constructors and type variables actually declared in the class. Both
    * static and instance members are included, but no inherited members are
    * included. The map is keyed by the simple names of the declarations.
    *
    * This does not include inherited members.
    */
@@ skipping 485 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});
 }