Revert r42145 to fix co19 tests

tests/language/bool_check_test.dart

-// Copyright (c) 2014, 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";
-
-bool typeChecksEnabled() {
-  try {
-    var i = 42;
-    String s = i;
-  } on TypeError catch (e) {
-    return true;
-  }
-  return false;
-}
-
-bool assertionsEnabled() {
-  try {
-    assert(false);
-    return false;
-  } on AssertionError catch (e) {
-    return true;
-  }
-  return false;
-}
-
-final bool typeChecksOn = typeChecksEnabled();
-final bool assertionsOn = assertionsEnabled();
-
-ifExpr(e) { if (e) return true; else return false; }
-bool ifNull() => ifExpr(null);
-bool ifString() => ifExpr("true");
-
-main() {
-  print("type checks: $typeChecksOn");
-  print("assertions:  $assertionsOn");
-
-  if (typeChecksOn) {
-    Expect.throws(ifNull, (e) => e is AssertionError);
-  }
-  if (assertionsOn && !typeChecksOn) {
-    Expect.throws(ifNull, (e) => e is AssertionError);
-  }
-  if (!typeChecksOn && !assertionsOn) {
-    Expect.identical(false, ifNull());
-  }
-
-  if (!typeChecksOn) {
-    Expect.identical(false, ifString());
-  }
-  if (typeChecksOn) {
-    Expect.throws(ifString, (e) => e is TypeError);
-  }
-}