Support "--checked" in pub run and global run.

test/run/runs_the_script_in_unchecked_mode_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:scheduled_test/scheduled_test.dart';
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 const SCRIPT = """
 main() {
   int a = true;
+  print("no checks");
 }
 """;
 
 main() {
-  integration('runs the script in checked mode by default', () {
+  integration('runs the script in unchecked mode by default', () {
     d.dir(appPath, [
       d.appPubspec(),
       d.dir("bin", [
         d.file("script.dart", SCRIPT)
       ])
     ]).create();
 
-    schedulePub(args: ["run", "bin/script"],
-        error: contains("'bool' is not a subtype of type 'int' of 'a'"),
-        exitCode: 255);
+    schedulePub(args: ["run", "bin/script"], output: contains("no checks"));
   });
 }