Change IllegalArgumentException to ArgumentError.

tests/corelib/expando_test.dart

Index: tests/corelib/expando_test.dart
diff --git a/tests/corelib/expando_test.dart b/tests/corelib/expando_test.dart
index f64fdc4509ad30a472bb05b74b371a96a7033822..7e006be083262d9e84126089d985cfb61c8ee7df 100644
--- a/tests/corelib/expando_test.dart
+++ b/tests/corelib/expando_test.dart
@@ -64,17 +64,17 @@ class ExpandoTest {
     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);
   }
 }