Change IllegalArgumentException to ArgumentError.

pkg/unittest/test/matchers_test.dart

Index: pkg/unittest/test/matchers_test.dart
diff --git a/pkg/unittest/test/matchers_test.dart b/pkg/unittest/test/matchers_test.dart
index 67aac3c83ce0d1eb78b6c2fd7410558f0f81c650..90501d6176a9956bd22714ff91849c31e69de604 100644
--- a/pkg/unittest/test/matchers_test.dart
+++ b/pkg/unittest/test/matchers_test.dart
@@ -95,14 +95,14 @@ void main() {
         "but:  exception <Exception> does not match FormatException.");
     });
 
-    test('throwsIllegalArgumentException', () {
-      shouldPass(() { throw new IllegalArgumentException(''); },
-          throwsIllegalArgumentException);
+    test('throwsArgumentError', () {
+      shouldPass(() { throw new ArgumentError(''); },
+          throwsArgumentError);
       shouldFail(() { throw new Exception(); },
-          throwsIllegalArgumentException,
-        "Expected: throws an exception which matches IllegalArgumentException "
+          throwsArgumentError,
+        "Expected: throws an exception which matches ArgumentError "
         "but:  exception <Exception> does not match "
-            "IllegalArgumentException.");
+            "ArgumentError.");
     });
 
     test('throwsIllegalJSRegExpException', () {