Make the values of Platform.executable and Platform.script available to all isolates

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 String _version();
 
   static int get numberOfProcessors => _numberOfProcessors();
   static String get pathSeparator => _pathSeparator();
   static String get operatingSystem => _operatingSystem();
 
   static String get localHostname {
     var result = _localHostname();
     if (result is OSError) {
       throw result;
     } else {
       return result;
     }
   }
 
+  static String get executable {

[Bill Hesse, 2013/08/07 13:39:44]

_executable() can never return null.  It returns a string, or it throws an
exception.

It almost seems like we could do
static String executable = _executable();
except that we may have no guarantee that the initialization is lazy on
platforms where _executable() throws an exception.

So, unless we cache explicitly with
get executable {
  if (executableCache == null) {
    executableCache = _executable();
  }
  return executableCache;
}

we might as well just call _executable() from Platform.executable.  This
function does nothing.

[Søren Gjesse, 2013/08/07 14:37:46]

Initially I was expecting to handle NULL, but it can never happen. Changed to be
just

static String executable = _executable();

+    var executable = _executable();
+    return executable != null ? executable : "";
+  }
+
   static Map<String, String> get environment {
     var env = _environment();
     if (env is OSError) {
       throw env;
     } else {
       var isWindows = operatingSystem == 'windows';
       var result = isWindows ? new _CaseInsensitiveStringMap() : new Map();
       for (var str in env) {
         // When running on Windows through cmd.exe there are strange
         // environment variables that are used to record the current
@@ skipping 44 matching lines @@
   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;
 
   Map<String, V> _map;
 }