Keep event page alive when there's some Pepper plugin on it.

ppapi/tests/extensions/load_unload/background.js

+// Copyright 2015 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.
+
+var nacl = null;
+
+function loadNaClModule() {
+  nacl = document.createElement('embed');
+  nacl.addEventListener('load', onNaClModuleLoaded, true);
+  nacl.type = 'application/x-nacl';
+  nacl.width = 0;
+  nacl.height = 0;
+  nacl.src = 'ppapi_tests_extensions_load_unload.nmf';
+  document.body.appendChild(nacl);
+
+  // Request the offsetTop property to force a relayout. As of Apr 10, 2014
+  // this is needed if the module is being loaded in a background page (see
+  // crbug.com/350445).
+  nacl.offsetTop;
+}
+
+function detachNaClModule() {
+  document.body.removeChild(nacl);
+  nacl = null;
+}
+
+function onNaClModuleLoaded() {
+  chrome.test.sendMessage("nacl_module_loaded");
+}
+
+chrome.browserAction.onClicked.addListener(function(tab) {
+  if (!nacl)
+    loadNaClModule();
+  else
+    detachNaClModule();
+});