Compute absolute script path at isolate startup.

sdk/lib/io/platform_impl.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.
 
 part of dart.io;
 
 class _Platform {
   external static int _numberOfProcessors();
   external static String _pathSeparator();
   external static String _operatingSystem();
   external static _localHostname();
   external static _executable();
   external static _environment();
   external static List<String> _executableArguments();
   external static String _packageRoot();
   external static String _version();
 
   static String executable = _executable();
   static String packageRoot = _packageRoot();
 
   // Cache the OS environemnt. This can be an OSError instance if
   // retrieving the environment failed.
   static var _environmentCache;
 
   static int get numberOfProcessors => _numberOfProcessors();
   static String get pathSeparator => _pathSeparator();
   static String get operatingSystem => _operatingSystem();
-  static Uri script = _script();
-  static Uri _script() {
-    // The embedder (Dart executable) creates the Platform._nativeScript field.
-    var s = Platform._nativeScript;
-    if (s.startsWith('http:') ||
-        s.startsWith('https:') ||
-        s.startsWith('file:')) {
-      return Uri.parse(s);
+  static Uri script;
+
+  // This script singleton is written to by the embedder if applicable.
+  static String set _nativeScript(String path) {
+    if (path.startsWith('http:') ||
+        path.startsWith('https:') ||
+        path.startsWith('file:')) {
+      script = Uri.parse(path);
     } else {
-      return Uri.base.resolveUri(new Uri.file(s));
+      script = Uri.base.resolveUri(new Uri.file(path));
     }
   }
 
   static String get localHostname {
     var result = _localHostname();
     if (result is OSError) {
       throw result;
     } else {
       return result;
     }
@@ skipping 59 matching lines @@
   V remove(String key) => _map.remove(key.toUpperCase());
   void clear() => _map.clear();
   void forEach(void f(String key, V value)) => _map.forEach(f);
   Iterable<String> get keys => _map.keys;
   Iterable<V> get values => _map.values;
   int get length => _map.length;
   bool get isEmpty => _map.isEmpty;
   bool get isNotEmpty => _map.isNotEmpty;
   String toString() => _map.toString();
 }