Revert "Remove Expect from core library."

tests/compiler/dart2js_native/native_novel_html_test.dart

 // Copyright (c) 2011, 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.
 
-import "package:expect/expect.dart";
-
 // Test to see if novel HTML tags are interpreted as HTMLElement.
 
 class Element native "*HTMLElement" {
   String dartMethod(int x) => 'dartMethod(${nativeMethod(x+1)})';
   String nativeMethod(int x) native;
 }
 
 makeE() native;
 makeF() native;
 
@@ skipping 27 matching lines @@
   var e = makeE();
   Expect.equals('Goofy.nativeMethod(10)', e.nativeMethod(10));
   Expect.equals('dartMethod(Goofy.nativeMethod(11))', e.dartMethod(10));
 
   var f = makeF();
   Expect.throws(() => f.nativeMethod(20), (e) => e is NoSuchMethodError,
       'fake HTML Element must not run Dart method on native class');
   Expect.throws(() => f.dartMethod(20), (e) => e is NoSuchMethodError,
       'fake HTML Element must not run native method on native class');
 }