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

ppapi/tests/extensions/load_unload/load_unload.cc

+// 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.
+
+#include "ppapi/cpp/instance.h"
+#include "ppapi/cpp/module.h"
+
+namespace {
+
+class Module : public pp::Module {
+ public:
+  virtual pp::Instance* CreateInstance(PP_Instance instance) {
+    return new pp::Instance(instance);
+  }
+};
+
+}  // namespace
+
+namespace pp {
+
+Module* CreateModule() {
+  return new ::Module();
+}
+
+}  // namespace pp