Disable modal JavaScript dialogs for platform apps.

chrome/test/data/extensions/platform_apps/modal_dialogs/background.js

+// Copyright (c) 2012 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.
+
+chrome.test.runTests([
+  function testAlert() {
+    alert("You shouldn't see this.... woot!");
+    chrome.test.succeed();
+  },
+
+  function testConfirm() {
+    chrome.test.assertFalse(confirm("Should this test fail?"));
+    chrome.test.succeed();
+  },
+
+  function testPrompt() {
+    chrome.test.assertEq(null, prompt("Return null to pass!"));
+    chrome.test.succeed();
+  }
+]);