Fix attributeChanged signature in WebUI (needs latest cherry-pick of custom

lib/testing/render_test.dart

Index: lib/testing/render_test.dart
diff --git a/lib/testing/render_test.dart b/lib/testing/render_test.dart
index a1fae296f1d9be9f245d7af98bed7e5bbd946154..c433f458750d4b7f87fc7fb25b6a25481a706571 100644
--- a/lib/testing/render_test.dart
+++ b/lib/testing/render_test.dart
@@ -17,7 +17,7 @@ void renderTests(String baseDir, String inputDir, String expectedDir,
     String outDir, {List<String> arguments, String script, String pattern,
     bool deleteDir: true}) {
   if (arguments == null) arguments = [];
-  if (script == null) script = Platform.script.toString();
+  if (script == null) script = Platform.script.path;
 
   var filePattern = new RegExp(pattern != null ? pattern
       : (arguments.length > 0 ? arguments.removeAt(0) : '.'));