Add fields to platform library, implement them on runtime dart.

tests/standalone/io/uri_platform_test.dart

Index: tests/standalone/io/uri_platform_test.dart
diff --git a/tests/standalone/io/uri_platform_test.dart b/tests/standalone/io/uri_platform_test.dart
index cc677606eababae1fe6a2fca603a4b04a7f00ad3..da09e998bd7cccfe42e3df5019ec9d81c512a9b8 100644
--- a/tests/standalone/io/uri_platform_test.dart
+++ b/tests/standalone/io/uri_platform_test.dart
@@ -4,9 +4,10 @@
 
 import "package:expect/expect.dart";
 import "dart:io";

[Anders Johnsen, 2013/10/24 08:30:08]

remove io import, and enable for dart2js.

[Bill Hesse, 2013/10/24 13:43:43]

Done.

+import "dart:platform" as platform;
 
 main() {
-  if (Platform.isWindows) {
+  if (platform.isWindows) {
     Expect.equals("a\\b", Uri.parse("a/b").toFilePath());
     Expect.equals("a\\b\\", Uri.parse("a/b/").toFilePath());
     Expect.equals("a b", Uri.parse("a%20b").toFilePath());
@@ -38,5 +39,5 @@ main() {
   }
 
   Expect.equals(Uri.base,
-                new Uri.file(Directory.current.path + Platform.pathSeparator));
+                new Uri.file(Directory.current.path + platform.pathSeparator));
 }