Implement "pinned" mode in ash.

ash/common/wm/always_on_top_controller.cc

 // Copyright (c) 2012 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 "ash/common/wm/always_on_top_controller.h"
 
 #include "ash/common/shell_window_ids.h"
 #include "ash/common/wm/workspace/workspace_layout_manager.h"
 #include "ash/common/wm/workspace/workspace_layout_manager_delegate.h"
+#include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
 #include "ash/common/wm_window_property.h"
 #include "base/memory/ptr_util.h"
 
 namespace ash {
 
 AlwaysOnTopController::AlwaysOnTopController(WmWindow* viewport)
     : always_on_top_container_(viewport) {
   always_on_top_container_->SetLayoutManager(
       base::WrapUnique(new WorkspaceLayoutManager(viewport, nullptr)));
+  WmShell::Get()->AddShellObserver(GetLayoutManager());
   // Container should be empty.
   DCHECK(always_on_top_container_->GetChildren().empty());
   always_on_top_container_->AddObserver(this);
 }
 
 AlwaysOnTopController::~AlwaysOnTopController() {
-  if (always_on_top_container_)
+  if (always_on_top_container_) {
     always_on_top_container_->RemoveObserver(this);
+    WmShell::Get()->RemoveShellObserver(GetLayoutManager());
+  }
 }
 
 WmWindow* AlwaysOnTopController::GetContainer(WmWindow* window) const {
   DCHECK(always_on_top_container_);
   if (window->GetBoolProperty(WmWindowProperty::ALWAYS_ON_TOP))
     return always_on_top_container_;
   return always_on_top_container_->GetRootWindow()->GetChildByShellWindowId(
       kShellWindowId_DefaultContainer);
 }
 
 // TODO(rsadam@): Refactor so that this cast is unneeded.
 WorkspaceLayoutManager* AlwaysOnTopController::GetLayoutManager() const {
   return static_cast<WorkspaceLayoutManager*>(
       always_on_top_container_->GetLayoutManager());
 }
 
 void AlwaysOnTopController::SetLayoutManagerForTest(
     std::unique_ptr<WorkspaceLayoutManager> layout_manager) {
+  WmShell::Get()->RemoveShellObserver(GetLayoutManager());
   always_on_top_container_->SetLayoutManager(std::move(layout_manager));
+  WmShell::Get()->AddShellObserver(GetLayoutManager());
 }
 
 void AlwaysOnTopController::OnWindowTreeChanged(
     WmWindow* window,
     const TreeChangeParams& params) {
   if (params.old_parent == always_on_top_container_)
     params.target->RemoveObserver(this);
   else if (params.new_parent == always_on_top_container_)
     params.target->AddObserver(this);
 }
 
 void AlwaysOnTopController::OnWindowPropertyChanged(WmWindow* window,
                                                     WmWindowProperty property) {
   if (window != always_on_top_container_ &&
       property == WmWindowProperty::ALWAYS_ON_TOP) {
     DCHECK(window->GetType() == ui::wm::WINDOW_TYPE_NORMAL ||
            window->GetType() == ui::wm::WINDOW_TYPE_POPUP);
     WmWindow* container = GetContainer(window);
     if (window->GetParent() != container)
       container->AddChild(window);
   }
 }
 
 void AlwaysOnTopController::OnWindowDestroying(WmWindow* window) {
   if (window == always_on_top_container_) {
     always_on_top_container_->RemoveObserver(this);
+    WmShell::Get()->RemoveShellObserver(GetLayoutManager());
     always_on_top_container_ = nullptr;
   }
 }
 
 }  // namespace ash