Allow Platform.executable for JIT app snapshots.

tests/standalone/io/addlatexhash_test.dart

 #!/usr/bin/env 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.
 
 // testing ../../../tools/addlatexhash.dart
 
 import 'dart:io';
 import 'package:path/path.dart' as path;
 import '../../../tools/addlatexhash.dart';
 
-final scriptDir = path.dirname(path.fromUri(Platform.script));
-final dartRootDir = path.dirname(path.dirname(path.dirname(scriptDir)));
+final execDir = path.dirname(path.fromUri(Platform.executable));
+final dartRootDir = path.dirname(path.dirname(execDir));
 final dartRootPath = dartRootDir.toString();
 
 List<String> packageOptions() {
   if (Platform.packageRoot != null) {
     return <String>['--package-root=${Platform.packageRoot}'];
   } else if (Platform.packageConfig != null) {
     return <String>['--packages=${Platform.packageConfig}'];
   } else {
     return <String>[];
   }
@@ skipping 189 matching lines @@
 main([args]) {
   testCutMatch();
   testSisp();
 
   runWithTempDir(testSameHash);
   // latex and dvi2tty are not installed in the standard test environment
   if (args.length > 0 && args[0] == "local") {
     runWithTempDir(testSameDVI);
   }
 }