Revert "Remove Expect from core library."

tests/standalone/debugger/basic_debugger_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.
 
 // This test forks a second vm process that runs this dart script as
 // a debug target.
 // Run this test with option --wire to see the json messages sent
 // between the processes.
 // Run this test with option --verbose to see the stdout and stderr output
 // of the debug target process.
 
-import "package:expect/expect.dart";
 import "debug_lib.dart";
 
 bar(x) {
   print(x);
 }
 
 foo(i) {
   bar("baz");
   print(i);
 }
@@ skipping 12 matching lines @@
   MatchFrame(0, "main"),  // Top frame in trace is function "main".
   Step(),
   Breakpoint(function: "main"),
   SetBreakpoint(15),  // Set breakpoint a line 15, in function bar.
   Resume(),
   Breakpoint(function: "bar"),
   MatchFrames(["bar", "foo", "main"]),
   MatchFrame(1, "foo"),
   Resume(),
 ];