Wrap Location object on Firefox.

tests/html/location_test.dart

+#library('LocationTest');
+#import('../../lib/unittest/unittest.dart');
+#import('../../lib/unittest/html_config.dart');
+#import('dart:html');
+
+main() {
+  useHtmlConfiguration();
+
+  test('location hash', () {
+      final location = window.location;
+      Expect.isTrue(location is Location);
+
+      // The only navigation we dare try is hash.
+      location.hash = 'hello';
+      var h = location.hash;
+      Expect.equals('#hello', h);
+    });
+}