Speed up interop patch file creation

tools/dartium/generate_app/generate_cached_patches.dart

+// Copyright (c) 2013, 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.
+
+import "dart:js" as js;
+
+void main() {
+  try {
+    var cached_files = js.createCachedPatchesFile();
+    print("$cached_files");
+  } catch (e) {
+    var workedElem = document.querySelector("#worked");
+    var failedElem = document.querySelector("#failed");
+    workedElem.style.dispay = 'none';
+    failedElem.style.visibility = 'inline';
+  }
+}
+