Remove need to instantiate Platform and make methods static.

tests/standalone/src/io/DirectoryTest.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.
 //
 // Directory listing test.
 
 #import("dart:io");
 #import("dart:isolate");
 
 class DirectoryTest {
@@ skipping 304 matching lines @@
     } else {
       emptyTemplateTestRunning = true;
       stage3();
     }
   }
 
   static void testCreateDeleteTemp() {
     Directory tempDirectory = new Directory("");
     tempDirectory.createTemp(() {
       String filename = tempDirectory.path +
-          new Platform().pathSeparator() + "dart_testfile";
+          Platform.pathSeparator() + "dart_testfile";
       File file = new File(filename);
       Expect.isFalse(file.existsSync());
       file.onError = (e) {
         Expect.fail("testCreateTemp file.onError called: $e");
       };
       file.create(() {
         file.exists((bool exists) {
           Expect.isTrue(exists);
           // Try to delete the directory containing the file - should throw.
           Expect.throws(tempDirectory.deleteSync);
           Expect.isTrue(tempDirectory.existsSync());
 
           // Delete the file, and then delete the directory.
           file.delete(() {
             tempDirectory.deleteSync();
             Expect.isFalse(tempDirectory.existsSync());
           });
         });
       });
     });
   }
 
   static void testCurrent() {
     Directory current = new Directory.current();
-    if (new Platform().operatingSystem() != "windows") {
+    if (Platform.operatingSystem() != "windows") {
       Expect.equals("/", current.path.substring(0, 1));
     }
   }
 
   static void testMain() {
     testListing();
     testListNonExistent();
     testListTooLongName();
     testDeleteNonExistent();
     testDeleteTooLongName();
@@ skipping 19 matching lines @@
     current.createTemp(createPhaseCallback);
   }
 
   void errorCallback(e) {
     Expect.fail("Error callback called in NestedTempDirectoryTest: $e");
   }
 
   void createPhaseCallback() {
     createdDirectories.add(current);
     int nestingDepth = 6;
-    var os = new Platform().operatingSystem();
+    var os = Platform.operatingSystem();
     if (os == "windows") nestingDepth = 2;
     if (createdDirectories.length < nestingDepth) {
       current = new Directory(
           current.path + "/nested_temp_dir_${createdDirectories.length}_");
       current.onError = errorCallback;
       current.createTemp(createPhaseCallback);
     } else {
       deletePhaseCallback();
     }
   }
 
   void deletePhaseCallback() {
     if (!createdDirectories.isEmpty()) {
       current = createdDirectories.removeLast();
       current.deleteSync();
       deletePhaseCallback();
     }
   }
 
   static void testMain() {
     new NestedTempDirectoryTest.run();
     new NestedTempDirectoryTest.run();
   }
 }
 
 
 String illegalTempDirectoryLocation() {
   // Determine a platform specific illegal location for a temporary directory.
-  var os = new Platform().operatingSystem();
+  var os = Platform.operatingSystem();
   if (os == "linux" || os == "macos") {
     return "/dev/zero/";
   }
   if (os == "windows") {
     return "*";
   }
   return null;
 }
 
 
@@ skipping 21 matching lines @@
   dir.createTemp(() => resultPort.toSendPort().send("success"));
 }
 
 
 main() {
   DirectoryTest.testMain();
   NestedTempDirectoryTest.testMain();
   testCreateTempErrorSync();
   testCreateTempError();
 }