Make reflectClass(dynamic) throw an illegal argument exception.

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 117 matching lines @@
  * obtain  mirrors on objects of the current isolate.
  */
 external InstanceMirror reflect(Object reflectee);
 
 /**
  * Let *C* be the original class declaration of the class
  * represented by [key]. 
  * This function returns a [ClassMirror] reflecting *C*.
  *
  * If [key] is not an instance of [Type] then this function
- * throws an [ArgumentError].
+ * throws an [ArgumentError]. If [key] is the Type dynamic,
+ * throws an [ArgumentError] because dynamic is not a class.
  *
  * Note that since one cannot obtain a [Type] object from
  * another isolate, this function can only be used to
  * obtain class mirrors on classes of the current isolate.
  */
 external ClassMirror reflectClass(Type key);
 
 /**
  * A [Mirror] reflects some Dart language entity.
  *
@@ skipping 1169 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});
 }