Revert "Delete the ViewManager and WindowManager services."

mojo/services/view_manager/cpp/view_tracker.cc

+// Copyright 2014 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 "view_manager/cpp/view_tracker.h"
+
+namespace mojo {
+
+ViewTracker::ViewTracker() {}
+
+ViewTracker::~ViewTracker() {
+  for (Views::iterator i = views_.begin(); i != views_.end(); ++i)
+    (*i)->RemoveObserver(this);
+}
+
+void ViewTracker::Add(View* view) {
+  if (views_.count(view))
+    return;
+
+  view->AddObserver(this);
+  views_.insert(view);
+}
+
+void ViewTracker::Remove(View* view) {
+  if (views_.count(view)) {
+    views_.erase(view);
+    view->RemoveObserver(this);
+  }
+}
+
+bool ViewTracker::Contains(View* view) {
+  return views_.count(view) > 0;
+}
+
+void ViewTracker::OnViewDestroying(View* view) {
+  DCHECK_GT(views_.count(view), 0u);
+  Remove(view);
+}
+
+}  // namespace mojo