fix windows bots with Platform.executable test

tests/standalone/io/platform_executable_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.
 //
 // Process test program to test process communication.
 
 library PlatformExecutableTest;
 
 import "dart:io";
 
+const _SCRIPT_KEY = '_test_script';
+
 void expectEquals(a, b) {
   if (a != b) {
     throw 'Expected: $a\n'
           '  Actual: $b';
   }
 }
 
 void verify(String exePath, {String altPath}) {
-  var env = {'SCRIPT': 'yes'};
+  var env = {_SCRIPT_KEY: 'yes'};
   if (altPath != null) {
     env['PATH'] = altPath;
   }
 
   var processResult = Process.runSync(exePath, [scriptPath],
       includeParentEnvironment: false, runInShell: true, environment: env);
 
   if (processResult.exitCode != 0) {
     throw 'Error with process\n'
           '$scriptPath'
           'Exit code: ${processResult.exitCode}\n'
           '   STDOUT: ${processResult.stdout}\n'
           '   STDERR: ${processResult.stderr}\n';
   }
 
   var result = processResult.stdout.trim();
   expectEquals(Platform.executable, result);
 }
 
 void testDartExecShouldNotBeInCurrentDir() {
   var type = FileSystemEntity.typeSync(platformExeName);
   expectEquals(FileSystemEntityType.NOT_FOUND, type);
 }
 
 void testShouldFailOutsidePath() {
   var threw = false;
   try {
-    Process.runSync(platformExeName, [scriptPath], 
-      includeParentEnvironment: false, environment: {'SCRIPT': 'yes'});
+    Process.runSync(platformExeName, [platformExeName], 

[Søren Gjesse, 2015/05/26 07:27:54]

Why are you passing [platformExeName] here?

+      includeParentEnvironment: false, environment: {_SCRIPT_KEY: 'yes'});
   } catch (_) {
     threw = true;
   }
 
-  expectEquals(true, threw);
+  if (!threw) {
+    throw 'Expected running the dart executable – "$platformExeName" without'
+          ' the parent environment or path to fail.';
+  }
 }
 
 void testShouldSucceedWithSourcePlatformExecutable() {
   //print('*** Running normally');
   verify(Platform.executable);
 }
 
 void testExeSymLinked(Directory dir) {
   var dirUri = new Uri.directory(dir.path);
   var link = new Link.fromUri(dirUri.resolve('dart_exe_link'));
@@ skipping 60 matching lines @@
 }
 
 String get platformExeName {
   var raw = new Uri.file(Platform.executable);
   return raw.pathSegments.last;
 }
 
 String get scriptPath => Platform.script.toFilePath();
 
 void main() {
-  if (Platform.environment.containsKey('SCRIPT')) {
+  if (Platform.environment.containsKey(_SCRIPT_KEY)) {
     print(Platform.executable);
     return;
   }
 
   testDartExecShouldNotBeInCurrentDir();
   testShouldSucceedWithSourcePlatformExecutable(); /// 00: ok
   withTempDir(testExeSymLinked); /// 01: ok
   withTempDir(testExeDirSymLinked); /// 02: ok
   testPathToSDKDir(); /// 03: ok
   withTempDir(testPathPointsToSymLinkedSDKPath); /// 04: ok
   withTempDir(testPathToDirWithExeSymLinked); /// 05: ok
   testShouldFailOutsidePath(); /// 06: ok
 }