Revert "Remove Expect from core library."

tests/standalone/io/process_invalid_arguments_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 that invalid arguments throw exceptions.
 
-import "package:expect/expect.dart";
 import "dart:io";
 
 void main() {
   Expect.throws(() => Process.start(["true"], []),
                 (e) => e is ArgumentError);
   Expect.throws(() => Process.start("true", "asdf"),
                 (e) => e is ArgumentError);
   Expect.throws(() => Process.start("true", ["asdf", 1]),
                 (e) => e is ArgumentError);
   Expect.throws(() => Process.run(["true"], [], null),
@@ skipping 10 matching lines @@
                 (e) => e is ArgumentError);
   options = new ProcessOptions();
   options.stdoutEncoding = 23;
   Expect.throws(() => Process.run("true", [], options),
                 (e) => e is ArgumentError);
   options = new ProcessOptions();
   options.stderrEncoding = 23;
   Expect.throws(() => Process.run("true", [], options),
                 (e) => e is ArgumentError);
 }