Remove Expect from core library.

tests/html/inner_frame_test.dart

 library InnerFrameTest;
+import "package:expect/expect.dart";
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 main() {
   if (window != window.top) {
     // Child frame.
 
     // The child's frame should not be able to access its parent's
     // document.
@@ skipping 99 matching lines @@
 
   test('parent', () {
       validate('parent', () {
         var div = document.query('#illegalParent');
 
         // Ensure that this parent frame was not modified by its child.
         expect(div, isNull);
       });
     });
 }