MD WebUI: Remove WebUI test focus hack by moving to interactive ui tests

chrome/test/data/webui/polymer_interactive_ui_test.js

Index: chrome/test/data/webui/polymer_interactive_ui_test.js
diff --git a/chrome/test/data/webui/polymer_interactive_ui_test.js b/chrome/test/data/webui/polymer_interactive_ui_test.js
new file mode 100644
index 0000000000000000000000000000000000000000..8737533e91db7e3659e8858f6bc84f4c188294f1
--- /dev/null
+++ b/chrome/test/data/webui/polymer_interactive_ui_test.js
@@ -0,0 +1,22 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+GEN_INCLUDE(['polymer_browser_test_base.js']);
+
+GEN('#include "chrome/browser/ui/browser.h"');
+GEN('#include "chrome/browser/ui/tabs/tab_strip_model.h"');
+GEN('#include "content/public/browser/web_contents.h"');
+
+function PolymerInteractiveUITest() {}
+
+PolymerInteractiveUITest.prototype = {
+  __proto__: PolymerTest.prototype,
+
+  testGenPreamble: function() {
+    // Must explicitly focus the web contents before running the test on Mac.
+    // See: https://crbug.com/642467.
+    GEN('  browser()->tab_strip_model()->GetActiveWebContents()->Focus();');
+  },
+
+};