[Aura] Support always-on-top top level window.

ui/aura_shell/always_on_top_controller.cc

Index: ui/aura_shell/always_on_top_controller.cc
diff --git a/ui/aura_shell/always_on_top_controller.cc b/ui/aura_shell/always_on_top_controller.cc
new file mode 100644
index 0000000000000000000000000000000000000000..177deb31a654b66e7d1a3f6ad6bd49b68b769187
--- /dev/null
+++ b/ui/aura_shell/always_on_top_controller.cc
@@ -0,0 +1,80 @@
+// Copyright (c) 2011 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 "ui/aura_shell/always_on_top_controller.h"
+
+#include "ui/aura/client/aura_constants.h"
+#include "ui/aura/window.h"
+#include "ui/aura/window_types.h"
+
+namespace aura_shell {
+namespace internal {
+
+AlwaysOnTopController::AlwaysOnTopController()
+    : default_container_(NULL),
+      always_on_top_container_(NULL) {
+}
+
+AlwaysOnTopController::~AlwaysOnTopController() {
+  if (default_container_)
+    default_container_->RemoveObserver(this);
+  if (always_on_top_container_)
+    always_on_top_container_->RemoveObserver(this);
+}
+
+void AlwaysOnTopController::SetContainers(aura::Window* default_container,
+    aura::Window* always_on_top_container) {
+  // Both containers should have no children.
+  DCHECK(default_container->children().empty());
+  DCHECK(always_on_top_container->children().empty());
+
+  // We are not handling any containers yet.
+  DCHECK(default_container_ == NULL && always_on_top_container_ == NULL);
+
+  default_container_ = default_container;
+  default_container_->AddObserver(this);
+
+  always_on_top_container_ = always_on_top_container;
+  always_on_top_container_->AddObserver(this);
+}
+
+aura::Window* AlwaysOnTopController::GetContainer(aura::Window* window) const {
+  DCHECK(default_container_ && always_on_top_container_);
+  return !window->GetProperty(aura::kAlwaysOnTopKey) ? default_container_ :
+                                                       always_on_top_container_;
+}
+
+void AlwaysOnTopController::OnWindowAdded(aura::Window* child) {
+  // Observe direct child of the containers.
+  if (child->parent() == default_container_ ||
+      child->parent() == always_on_top_container_) {
+    child->AddObserver(this);
+  }
+}
+
+void AlwaysOnTopController::OnWillRemoveWindow(aura::Window* child) {
+  child->RemoveObserver(this);
+}
+
+void AlwaysOnTopController::OnPropertyChanged(aura::Window* window,
+                                              const char* name,
+                                              void* old) {
+  if (name == aura::kAlwaysOnTopKey) {
+    DCHECK(window->type() == aura::WINDOW_TYPE_NORMAL ||
+           window->type() == aura::WINDOW_TYPE_POPUP);
+    aura::Window* container = GetContainer(window);
+    if (window->parent() != container)
+      container->AddChild(window);
+  }
+}
+
+void AlwaysOnTopController::OnWindowDestroyed(aura::Window* window) {
+  if (window == default_container_)
+    default_container_ = NULL;
+  if (window == always_on_top_container_)
+    always_on_top_container_ = NULL;
+}
+
+}  // namespace internal
+}  // namespace aura_shell