Demo UI made with a help of WUG toolkit (DO NOT SEND TO CQ).

chrome/browser/ui/webui/demo_ui/reuse/reuse_demo.cc

Index: chrome/browser/ui/webui/demo_ui/reuse/reuse_demo.cc
diff --git a/chrome/browser/ui/webui/demo_ui/reuse/reuse_demo.cc b/chrome/browser/ui/webui/demo_ui/reuse/reuse_demo.cc
new file mode 100644
index 0000000000000000000000000000000000000000..690e5a583934d009d6bb9716dfd83411423aade3
--- /dev/null
+++ b/chrome/browser/ui/webui/demo_ui/reuse/reuse_demo.cc
@@ -0,0 +1,39 @@
+// 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 "chrome/browser/ui/webui/demo_ui/reuse/reuse_demo.h"
+
+ReuseDemo::ReuseDemo() {
+}
+
+ReuseDemo::~ReuseDemo() {
+  GetLeftEvents()->RemoveObserver(this);
+  GetRightEvents()->RemoveObserver(this);
+}
+
+void ReuseDemo::OnAfterChildrenReady() {
+  GetLeftEvents()->AddObserver(this);
+  GetRightEvents()->AddObserver(this);
+  EventsCounterChanged();
+}
+
+void ReuseDemo::EventsCounterChanged() {
+  GetContextEditor().SetInteger(
+      kContextKeyTotalClicks,
+      GetLeftEvents()->GetEventCounter() + GetRightEvents()->GetEventCounter());
+}
+
+EventsDemo* ReuseDemo::GetLeftEvents() const {
+  return static_cast<EventsDemo*>(gen::ReuseDemoViewModel::GetLeftEvents());
+}
+
+EventsDemo* ReuseDemo::GetRightEvents() const {
+  return static_cast<EventsDemo*>(gen::ReuseDemoViewModel::GetRightEvents());
+}
+
+void ReuseDemo::Register() {
+  SetFactory(
+      [](content::BrowserContext*)
+          -> gen::ReuseDemoViewModel* { return new ReuseDemo(); });
+}