Change IllegalArgumentException to ArgumentError.

tests/corelib/expando_test.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.
 
 class ExpandoTest {
   static Expando<int> visits;
 
   static testMain() {
     visits = new Expando<int>('visits');
     var legal = [ new Object(),
@@ skipping 46 matching lines @@
     expando[object] = 99;
     Expect.equals(99, expando[object]);
     Expect.equals(87, alternative[object]);
   }
 
   static testIllegal() {
     Expando<int> expando = new Expando<int>();
     Expect.throws(() => expando[null], (exception)
                   => exception is NullPointerException);
     Expect.throws(() => expando['string'], (exception)
-                  => exception is IllegalArgumentException);
+                  => exception is ArgumentError);
     Expect.throws(() => expando['string'], (exception)
-                  => exception is IllegalArgumentException);
+                  => exception is ArgumentError);
     Expect.throws(() => expando[42], (exception)
-                  => exception is IllegalArgumentException);
+                  => exception is ArgumentError);
     Expect.throws(() => expando[42.87], (exception)
-                  => exception is IllegalArgumentException);
+                  => exception is ArgumentError);
     Expect.throws(() => expando[true], (exception)
-                  => exception is IllegalArgumentException);
+                  => exception is ArgumentError);
     Expect.throws(() => expando[false], (exception)
-                  => exception is IllegalArgumentException);
+                  => exception is ArgumentError);
   }
 }
 
 main() => ExpandoTest.testMain();