Remove Expect from core library.

tests/standalone/io/process_broken_pipe_test.dart

 // Copyright (c) 2012, 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.
 //
 // Process test program to test closed stdin from child process.
 
+import "package:expect/expect.dart";
 import "dart:io";
 
 import "process_test_util.dart";
 
 main() {
   // Running dart without arguments makes it close right away.
   var future = Process.start(new Options().executable, []);
   future.then((process) {
     // Ignore error on stdin.
     process.stdin.onError = (e) => null;
 
     // Drain stdout and stderr.
     process.stdout.onData = () => process.stdout.read();
     process.stderr.onData = () => process.stderr.read();
 
     // Write to the stdin after the process is terminated to test
     // writing to a broken pipe.
     process.onExit = (code) {
       Expect.isFalse(process.stdin.write([0]));
     };
   });
 }