Compute absolute script path at isolate startup.

tests/standalone/io/platform_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.
 
 import "dart:async";
 import "dart:io";
 import "dart:isolate";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
 test() {
   Expect.isTrue(Platform.numberOfProcessors > 0);
   var os = Platform.operatingSystem;
   Expect.isTrue(os == "android" || os == "linux" || os == "macos" ||
       os == "windows");
   Expect.equals(Platform.isLinux, Platform.operatingSystem == "linux");
   Expect.equals(Platform.isMacOS, Platform.operatingSystem == "macos");
   Expect.equals(Platform.isWindows, Platform.operatingSystem == "windows");
   Expect.equals(Platform.isAndroid, Platform.operatingSystem == "android");
   var sep = Platform.pathSeparator;
   Expect.isTrue(sep == '/' || (os == 'windows' && sep == '\\'));
   var hostname = Platform.localHostname;
   Expect.isTrue(hostname is String && hostname != "");
   var environment = Platform.environment;
   Expect.isTrue(environment is Map<String, String>);
   Expect.isTrue(Platform.executable.contains('dart'));
+  // Move directory to be sure script is correct.
+  var oldDir = Directory.current;
+  Directory.current = Directory.current.parent;
   Expect.isTrue(Platform.script.path.
                 endsWith('tests/standalone/io/platform_test.dart'));
+  Expect.isTrue(Platform.script.path.startsWith(oldDir.path));
+  // Restore dir.
+  Directory.current = oldDir;
   Directory packageRoot = new Directory(Platform.packageRoot);
   Expect.isTrue(packageRoot.existsSync());
   Expect.isTrue(new Directory("${packageRoot.path}/expect").existsSync());
   Expect.isTrue(Platform.executableArguments.any(
       (arg) => arg.contains(Platform.packageRoot)));
 }
 
 void f(reply) {
   reply.send({"Platform.executable": Platform.executable,
               "Platform.script": Platform.script,
@@ skipping 17 matching lines @@
     Expect.listEquals(Platform.executableArguments,
                       results["Platform.executableArguments"]);
     asyncEnd();
   });
 }
 
 main() {
   test();
   testIsolate();
 }