Put two $ in front of top-level builtins, to not clash with member names. Otherwise, the global obj…

client/tests/client/dom/WindowEqTest.dart

Index: client/tests/client/dom/WindowEqTest.dart
===================================================================
--- client/tests/client/dom/WindowEqTest.dart	(revision 0)
+++ client/tests/client/dom/WindowEqTest.dart	(revision 0)
@@ -0,0 +1,12 @@
+#library('WindowEqualityTest');
+#import('../../../testing/unittest/unittest.dart');
+#import('dart:dom');
+
+main() {
+  var obfuscated = null;
+
+  test('notNull', () {
+      Expect.isNotNull(window);
+      Expect.isTrue(window != obfuscated);
+    });
+}