Modify the instance test to work with dart2js by using looser matching,

pkg/unittest/test/instance_test.dart

Index: pkg/unittest/test/instance_test.dart
===================================================================
--- pkg/unittest/test/instance_test.dart	(revision 25450)
+++ pkg/unittest/test/instance_test.dart	(working copy)
@@ -20,10 +20,9 @@
     test('throwsA', () {
       shouldPass(doesThrow, throwsA(equals('X')));
       shouldFail(doesThrow, throwsA(equals('Y')),
-          "Expected: throws 'Y' "
-          "Actual: <Closure: () => dynamic "
-              "from Function 'doesThrow': static.> "
-          "Which: threw 'X'");
+          matches("Expected: throws 'Y'.*"
+          "Actual: <Closure.*"
+          "Which: threw 'X'"));
     });
   });
 }