Adding a gray semi transparent backdrop behind the topmost window within the default container

This is part of the "always maximized" feature. Windows which cannot be maximized - or cannot be made to cover the entire screen should have a backdrop behind them which covers the desktop.

Tried various ways to implement this and this seems to be the best solution.

BUG=337567, 337563

Review URL: https://codereview.chromium.org/169643005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255863 0039d316-1c4b-4281-b951-d872f2087c98

11 files changed, 585 insertions, 21 deletions

diff --git a/ash/ash.gyp b/ash/ash.gyp
index b1f0e25..ac21917 100644
--- a/ash/ash.gyp
+++ b/ash/ash.gyp
@@ -540,6 +540,8 @@
         'wm/lock_state_observer.h',
         'wm/maximize_mode/maximize_mode_window_manager.cc',
         'wm/maximize_mode/maximize_mode_window_manager.h',        
+        'wm/maximize_mode/workspace_backdrop_delegate.cc',
+        'wm/maximize_mode/workspace_backdrop_delegate.h',
         'wm/mru_window_tracker.cc',
         'wm/mru_window_tracker.h',
         'wm/overlay_event_filter.cc',
@@ -643,6 +645,7 @@
         'wm/workspace/workspace_event_handler.h',
         'wm/workspace/workspace_layout_manager.cc',
         'wm/workspace/workspace_layout_manager.h',
+        'wm/workspace/workspace_layout_manager_delegate.h',
         'wm/workspace/workspace_types.h',
         'wm/workspace/workspace_window_resizer.cc',
         'wm/workspace/workspace_window_resizer.h',
@@ -969,6 +972,8 @@
         'wm/window_positioner_unittest.cc',
         'wm/window_state_unittest.cc',
         'wm/window_util_unittest.cc',
+        'wm/maximize_mode/workspace_backdrop_delegate.cc',
+        'wm/maximize_mode/workspace_backdrop_delegate.h',
         'wm/workspace/magnetism_matcher_unittest.cc',
         'wm/workspace/multi_window_resize_controller_unittest.cc',
         'wm/workspace/phantom_window_controller_unittest.cc',
diff --git a/ash/wm/maximize_mode/maximize_mode_window_manager.cc b/ash/wm/maximize_mode/maximize_mode_window_manager.cc
index cd42ba9..6858f36 100644
--- a/ash/wm/maximize_mode/maximize_mode_window_manager.cc
+++ b/ash/wm/maximize_mode/maximize_mode_window_manager.cc
@@ -4,9 +4,12 @@
 
 #include "ash/wm/maximize_mode/maximize_mode_window_manager.h"
 
+#include "ash/root_window_controller.h"
 #include "ash/shell.h"
-#include "ash/switchable_windows.h"
+#include "ash/shell_window_ids.h"
+#include "ash/wm/maximize_mode/workspace_backdrop_delegate.h"
 #include "ash/wm/mru_window_tracker.h"
+#include "ash/wm/workspace_controller.h"
 #include "ui/aura/window.h"
 #include "ui/gfx/screen.h"
 
@@ -14,7 +17,9 @@ namespace ash {
 namespace internal {
 
 MaximizeModeWindowManager::~MaximizeModeWindowManager() {
+  Shell::GetInstance()->RemoveShellObserver(this);
   Shell::GetScreen()->RemoveObserver(this);
+  EnableBackdropBehindTopWindowOnEachDisplay(false);
   RemoveWindowCreationObservers();
   RestoreAllWindows();
 }
@@ -23,6 +28,22 @@ int MaximizeModeWindowManager::GetNumberOfManagedWindows() {
   return initial_state_type_.size();
 }
 
+void MaximizeModeWindowManager::OnOverviewModeStarted() {
+  if (backdrops_hidden_)
+    return;
+
+  EnableBackdropBehindTopWindowOnEachDisplay(false);
+  backdrops_hidden_ = true;
+}
+
+void MaximizeModeWindowManager::OnOverviewModeEnded() {
+  if (!backdrops_hidden_)
+    return;
+
+  backdrops_hidden_ = false;
+  EnableBackdropBehindTopWindowOnEachDisplay(true);
+}
+
 void MaximizeModeWindowManager::OnWindowDestroying(aura::Window* window) {
   // If a known window gets destroyed we need to remove all knowledge about it.
   if (!IsContainerWindow(window))
@@ -65,10 +86,15 @@ void MaximizeModeWindowManager::OnDisplayRemoved(const gfx::Display& display) {
   DisplayConfigurationChanged();
 }
 
-MaximizeModeWindowManager::MaximizeModeWindowManager() {
+MaximizeModeWindowManager::MaximizeModeWindowManager()
+      : backdrops_hidden_(false) {
+  // TODO(skuhne): Turn off the overview mode and full screen modes before
+  // entering the MaximzieMode.
   MaximizeAllWindows();
   AddWindowCreationObservers();
+  EnableBackdropBehindTopWindowOnEachDisplay(true);
   Shell::GetScreen()->AddObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
 }
 
 void MaximizeModeWindowManager::MaximizeAllWindows() {
@@ -110,7 +136,6 @@ void MaximizeModeWindowManager::MaximizeAndTrackWindow(
       else
         window_state->SetRestoreBoundsInScreen(initial_rect);
       CenterWindow(window);
-      // TODO(skuhne): Add a background cover layer.
     } else {
       // Minimized windows can remain as they are.
       if (state != wm::WINDOW_STATE_TYPE_MINIMIZED)
@@ -128,7 +153,6 @@ void MaximizeModeWindowManager::RestoreAndForgetWindow(
   // Restore window if it can be restored.
   if (state != wm::WINDOW_STATE_TYPE_MAXIMIZED) {
     if (!CanMaximize(window)) {
-      // TODO(skuhne): Remove the background cover layer.
       if (window_state->HasRestoreBounds()) {
         // TODO(skuhne): If the system shuts down in maximized mode, the proper
         // restore coordinates should get saved.
@@ -187,19 +211,17 @@ void MaximizeModeWindowManager::CenterWindow(aura::Window* window) {
 
 void MaximizeModeWindowManager::AddWindowCreationObservers() {
   DCHECK(observed_container_windows_.empty());
-  // Observe window activations and switchable containers on all root windows
-  // for newly created windows during overview.
+  // Observe window activations/creations in the default containers on all root
+  // windows.
   aura::Window::Windows root_windows = Shell::GetAllRootWindows();
   for (aura::Window::Windows::const_iterator iter = root_windows.begin();
        iter != root_windows.end(); ++iter) {
-    for (size_t i = 0; i < kSwitchableWindowContainerIdsLength; ++i) {
-      aura::Window* container = Shell::GetContainer(*iter,
-          kSwitchableWindowContainerIds[i]);
-      DCHECK(observed_container_windows_.find(container) ==
-                observed_container_windows_.end());
-      container->AddObserver(this);
-      observed_container_windows_.insert(container);
-    }
+    aura::Window* container = Shell::GetContainer(*iter,
+        internal::kShellWindowId_DefaultContainer);
+    DCHECK(observed_container_windows_.find(container) ==
+              observed_container_windows_.end());
+    container->AddObserver(this);
+    observed_container_windows_.insert(container);
   }
 }
 
@@ -213,8 +235,10 @@ void MaximizeModeWindowManager::RemoveWindowCreationObservers() {
 }
 
 void MaximizeModeWindowManager::DisplayConfigurationChanged() {
+  EnableBackdropBehindTopWindowOnEachDisplay(false);
   RemoveWindowCreationObservers();
   AddWindowCreationObservers();
+  EnableBackdropBehindTopWindowOnEachDisplay(true);
 }
 
 bool MaximizeModeWindowManager::IsContainerWindow(aura::Window* window) {
@@ -222,5 +246,25 @@ bool MaximizeModeWindowManager::IsContainerWindow(aura::Window* window) {
              observed_container_windows_.end();
 }
 
+void MaximizeModeWindowManager::EnableBackdropBehindTopWindowOnEachDisplay(
+    bool enable) {
+  if (backdrops_hidden_)
+    return;
+  // Inform the WorkspaceLayoutManager that we want to show a backdrop behind
+  // the topmost window of its container.
+  Shell::RootWindowControllerList controllers =
+      Shell::GetAllRootWindowControllers();
+  for (Shell::RootWindowControllerList::iterator iter = controllers.begin();
+       iter != controllers.end(); ++iter) {
+    RootWindowController* controller = *iter;
+    aura::Window* container = Shell::GetContainer(
+        controller->root_window(),
+        internal::kShellWindowId_DefaultContainer);
+    controller->workspace_controller()->SetMaximizeBackdropDelegate(
+        scoped_ptr<WorkspaceLayoutManagerDelegate>(
+            enable ? new WorkspaceBackdropDelegate(container) : NULL));
+  }
+}
+
 }  // namespace internal
 }  // namespace ash
diff --git a/ash/wm/maximize_mode/maximize_mode_window_manager.h b/ash/wm/maximize_mode/maximize_mode_window_manager.h
index ba5d1bd..f8af8d0 100644
--- a/ash/wm/maximize_mode/maximize_mode_window_manager.h
+++ b/ash/wm/maximize_mode/maximize_mode_window_manager.h
@@ -9,6 +9,7 @@
 #include <set>
 
 #include "ash/ash_export.h"
+#include "ash/shell_observer.h"
 #include "ash/wm/window_state.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
@@ -27,12 +28,13 @@ namespace internal{
 // With the destruction of the manager all windows will be restored to their
 // original state.
 class ASH_EXPORT MaximizeModeWindowManager : public aura::WindowObserver,
-                                             public gfx::DisplayObserver {
+                                             public gfx::DisplayObserver,
+                                             public ShellObserver {
  public:
   // This should only be deleted by the creator (ash::Shell).
   virtual ~MaximizeModeWindowManager();
 
- // Returns the number of maximized & tracked windows by this manager.
+  // Returns the number of maximized & tracked windows by this manager.
   int GetNumberOfManagedWindows();
 
   // Overridden from WindowObserver:
@@ -48,6 +50,10 @@ class ASH_EXPORT MaximizeModeWindowManager : public aura::WindowObserver,
   virtual void OnDisplayAdded(const gfx::Display& display) OVERRIDE;
   virtual void OnDisplayRemoved(const gfx::Display& display) OVERRIDE;
 
+  // ShellObserver overrides:
+  void OnOverviewModeStarted();
+  void OnOverviewModeEnded();
+
  protected:
   friend class ash::Shell;
 
@@ -98,12 +104,18 @@ class ASH_EXPORT MaximizeModeWindowManager : public aura::WindowObserver,
   // Returns true when the |window| is a container window.
   bool IsContainerWindow(aura::Window* window);
 
+  // Add a backdrop behind the currently active window on each desktop.
+  void EnableBackdropBehindTopWindowOnEachDisplay(bool enable);
+
   // Every window which got touched by our window manager gets added here.
   WindowToStateType initial_state_type_;
 
   // All container windows which have to be tracked.
   std::set<aura::Window*> observed_container_windows_;
 
+  // True if all backdrops are hidden.
+  bool backdrops_hidden_;
+
   DISALLOW_COPY_AND_ASSIGN(MaximizeModeWindowManager);
 };
 
diff --git a/ash/wm/maximize_mode/workspace_backdrop_delegate.cc b/ash/wm/maximize_mode/workspace_backdrop_delegate.cc
new file mode 100644
index 0000000..e996fca
--- /dev/null
+++ b/ash/wm/maximize_mode/workspace_backdrop_delegate.cc
@@ -0,0 +1,154 @@
+// 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 "ash/wm/maximize_mode/workspace_backdrop_delegate.h"
+
+#include "ash/wm/window_animations.h"
+#include "ash/wm/window_util.h"
+#include "base/auto_reset.h"
+#include "ui/aura/window.h"
+#include "ui/compositor/layer.h"
+#include "ui/compositor/scoped_layer_animation_settings.h"
+#include "ui/views/background.h"
+#include "ui/views/corewm/window_util.h"
+#include "ui/views/widget/widget.h"
+
+namespace ash {
+
+namespace internal {
+
+namespace {
+
+// The opacity of the backdrop.
+const float kBackdropOpacity = 0.5f;
+
+}  // namespace
+
+WorkspaceBackdropDelegate::WorkspaceBackdropDelegate(aura::Window* container)
+    : background_(NULL),
+      container_(container),
+      in_restacking_(false) {
+  background_ = new views::Widget;
+  views::Widget::InitParams params(
+      views::Widget::InitParams::TYPE_WINDOW_FRAMELESS);
+  params.parent = container_;
+  params.bounds = container_->bounds();
+  params.layer_type = aura::WINDOW_LAYER_SOLID_COLOR;
+  // To disallow the MRU list from picking this window up it should not be
+  // activateable.
+  params.can_activate = false;
+  background_->Init(params);
+  background_->GetNativeView()->SetName("WorkspaceBackdropDelegate");
+  background_->GetNativeView()->layer()->SetColor(SK_ColorBLACK);
+  Show();
+  RestackBackdrop();
+  container_->AddObserver(this);
+}
+
+WorkspaceBackdropDelegate::~WorkspaceBackdropDelegate() {
+  container_->RemoveObserver(this);
+  ui::ScopedLayerAnimationSettings settings(
+      background_->GetNativeView()->layer()->GetAnimator());
+  background_->Close();
+  settings.AddObserver(views::corewm::CreateHidingWindowAnimationObserver(
+      background_->GetNativeView()));
+  background_->GetNativeView()->layer()->SetOpacity(0.0f);
+}
+
+void WorkspaceBackdropDelegate::OnWindowBoundsChanged(
+    aura::Window* window,
+    const gfx::Rect& old_bounds,
+    const gfx::Rect& new_bounds) {
+  // The container size has changed and the layer needs to be adapt to it.
+  AdjustToContainerBounds();
+}
+
+void WorkspaceBackdropDelegate::OnWindowAddedToLayout(aura::Window* child) {
+  RestackBackdrop();
+}
+
+void WorkspaceBackdropDelegate::OnWindowRemovedFromLayout(aura::Window* child) {
+  RestackBackdrop();
+}
+
+void WorkspaceBackdropDelegate::OnChildWindowVisibilityChanged(
+    aura::Window* child,
+    bool visible) {
+  RestackBackdrop();
+}
+
+void WorkspaceBackdropDelegate::OnWindowStackingChanged(aura::Window* window) {
+  RestackBackdrop();
+}
+
+void WorkspaceBackdropDelegate::OnPostWindowStateTypeChange(
+    wm::WindowState* window_state,
+    wm::WindowStateType old_type) {
+  RestackBackdrop();
+}
+
+void WorkspaceBackdropDelegate::RestackBackdrop() {
+  // Avoid recursive calls.
+  if (in_restacking_)
+    return;
+
+  aura::Window* window = GetCurrentTopWindow();
+  if (!window) {
+    // Hide backdrop since no suitable window was found.
+    background_->Hide();
+    return;
+  }
+  if (window == background_->GetNativeWindow() &&
+      background_->IsVisible()) {
+    return;
+  }
+  // We are changing the order of windows which will cause recursion.
+  base::AutoReset<bool> lock(&in_restacking_, true);
+  if (!background_->IsVisible())
+    Show();
+  // Since the backdrop needs to be immediately behind the window and the
+  // stacking functions only guarantee a "it's above or below", we need
+  // to re-arrange the two windows twice.
+  container_->StackChildAbove(background_->GetNativeView(), window);
+  container_->StackChildAbove(window, background_->GetNativeView());
+}
+
+aura::Window* WorkspaceBackdropDelegate::GetCurrentTopWindow() {
+  const aura::Window::Windows& windows = container_->children();
+  for (aura::Window::Windows::const_reverse_iterator window_iter =
+           windows.rbegin();
+       window_iter != windows.rend(); ++window_iter) {
+    aura::Window* window = *window_iter;
+    if (window->TargetVisibility() &&
+        window->type() == ui::wm::WINDOW_TYPE_NORMAL &&
+        ash::wm::CanActivateWindow(window))
+      return window;
+  }
+  return NULL;
+}
+
+void WorkspaceBackdropDelegate::AdjustToContainerBounds() {
+  // Cover the entire container window.
+  gfx::Rect target_rect(gfx::Point(0, 0), container_->bounds().size());
+  if (target_rect != background_->GetNativeWindow()->bounds()) {
+    // This needs to be instant.
+    ui::ScopedLayerAnimationSettings settings(
+        background_->GetNativeView()->layer()->GetAnimator());
+    settings.SetTransitionDuration(base::TimeDelta::FromMilliseconds(0));
+    background_->GetNativeWindow()->SetBounds(target_rect);
+    if (!background_->IsVisible())
+      background_->GetNativeView()->layer()->SetOpacity(kBackdropOpacity);
+  }
+}
+
+void WorkspaceBackdropDelegate::Show() {
+  background_->GetNativeView()->layer()->SetOpacity(0.0f);
+  background_->Show();
+  ui::ScopedLayerAnimationSettings settings(
+      background_->GetNativeView()->layer()->GetAnimator());
+  background_->GetNativeView()->layer()->SetOpacity(kBackdropOpacity);
+}
+
+}  // namespace internal
+}  // namespace ash
diff --git a/ash/wm/maximize_mode/workspace_backdrop_delegate.h b/ash/wm/maximize_mode/workspace_backdrop_delegate.h
new file mode 100644
index 0000000..02ba3a3
--- /dev/null
+++ b/ash/wm/maximize_mode/workspace_backdrop_delegate.h
@@ -0,0 +1,80 @@
+// 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.
+
+#ifndef ASH_WM_MAXIMIZE_MODE_WORKSPACE_BACKDROP_DELEGATE_H_
+#define ASH_WM_MAXIMIZE_MODE_WORKSPACE_BACKDROP_DELEGATE_H_
+
+#include "ash/wm/workspace/workspace_layout_manager_delegate.h"
+#include "ui/aura/window_observer.h"
+
+namespace aura {
+class Window;
+}
+
+namespace ui {
+class Layer;
+}
+
+namespace views {
+class Widget;
+}
+
+namespace ash {
+
+namespace internal {
+
+// A background which gets created for a container |window| and which gets
+// stacked behind the topmost window (within that container) covering the
+// entire container.
+class WorkspaceBackdropDelegate : public aura::WindowObserver,
+                                  public WorkspaceLayoutManagerDelegate {
+ public:
+  explicit WorkspaceBackdropDelegate(aura::Window* container);
+  virtual ~WorkspaceBackdropDelegate();
+
+  // WindowObserver overrides:
+  virtual void OnWindowBoundsChanged(aura::Window* window,
+                                     const gfx::Rect& old_bounds,
+                                     const gfx::Rect& new_bounds) OVERRIDE;
+
+  // WorkspaceLayoutManagerDelegate overrides:
+  virtual void OnWindowAddedToLayout(aura::Window* child) OVERRIDE;
+  virtual void OnWindowRemovedFromLayout(aura::Window* child) OVERRIDE;
+  virtual void OnChildWindowVisibilityChanged(aura::Window* child,
+                                              bool visible) OVERRIDE;
+  virtual void OnWindowStackingChanged(aura::Window* window) OVERRIDE;
+  virtual void OnPostWindowStateTypeChange(
+      wm::WindowState* window_state,
+      wm::WindowStateType old_type) OVERRIDE;
+
+ private:
+  // Restack the backdrop relatively to the other windows in the container.
+  void RestackBackdrop();
+
+  // Returns the current visible top level window in the container.
+  aura::Window* GetCurrentTopWindow();
+
+  // Position & size the background over the container window.
+  void AdjustToContainerBounds();
+
+  // Show the overlay.
+  void Show();
+
+  // The background which covers the rest of the screen.
+  views::Widget* background_;
+
+  // The window which is being "maximized".
+  aura::Window* container_;
+
+  // If true, the |RestackOrHideWindow| might recurse.
+  bool in_restacking_;
+
+  DISALLOW_COPY_AND_ASSIGN(WorkspaceBackdropDelegate);
+};
+
+}  // namespace internal
+
+}  // namespace ash
+
+#endif  // ASH_WM_MAXIMIZE_MODE_WORKSPACE_BACKDROP_DELEGATE_H_
diff --git a/ash/wm/workspace/workspace_layout_manager.cc b/ash/wm/workspace/workspace_layout_manager.cc
index 1aaebf9..687324c 100644
--- a/ash/wm/workspace/workspace_layout_manager.cc
+++ b/ash/wm/workspace/workspace_layout_manager.cc
@@ -17,6 +17,7 @@
 #include "ash/wm/window_state.h"
 #include "ash/wm/window_util.h"
 #include "ash/wm/wm_event.h"
+#include "ash/wm/workspace/workspace_layout_manager_delegate.h"
 #include "ui/aura/client/activation_client.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/window.h"
@@ -50,12 +51,8 @@ WorkspaceLayoutManager::WorkspaceLayoutManager(aura::Window* window)
 WorkspaceLayoutManager::~WorkspaceLayoutManager() {
   if (root_window_)
     root_window_->RemoveObserver(this);
-  for (WindowSet::const_iterator i = windows_.begin();
-       i != windows_.end();
-       ++i) {
+  for (WindowSet::const_iterator i = windows_.begin(); i != windows_.end(); ++i)
     (*i)->RemoveObserver(this);
-    wm::GetWindowState(*i)->RemoveObserver(this);
-  }
   Shell::GetInstance()->RemoveShellObserver(this);
   Shell::GetInstance()->activation_client()->RemoveObserver(this);
 }
@@ -64,6 +61,11 @@ void WorkspaceLayoutManager::SetShelf(internal::ShelfLayoutManager* shelf) {
   shelf_ = shelf;
 }
 
+void WorkspaceLayoutManager::SetMaximizeBackdropDelegate(
+    scoped_ptr<WorkspaceLayoutManagerDelegate> delegate) {
+  backdrop_delegate_.reset(delegate.release());
+}
+
 //////////////////////////////////////////////////////////////////////////////
 // WorkspaceLayoutManager, aura::LayoutManager implementation:
 
@@ -76,6 +78,8 @@ void WorkspaceLayoutManager::OnWindowAddedToLayout(Window* child) {
   window_state->AddObserver(this);
   UpdateShelfVisibility();
   UpdateFullscreenState();
+  if (backdrop_delegate_)
+    backdrop_delegate_->OnWindowAddedToLayout(child);
   WindowPositioner::RearrangeVisibleWindowOnShow(child);
 }
 
@@ -91,6 +95,8 @@ void WorkspaceLayoutManager::OnWillRemoveWindowFromLayout(Window* child) {
 void WorkspaceLayoutManager::OnWindowRemovedFromLayout(Window* child) {
   UpdateShelfVisibility();
   UpdateFullscreenState();
+  if (backdrop_delegate_)
+    backdrop_delegate_->OnWindowRemovedFromLayout(child);
 }
 
 void WorkspaceLayoutManager::OnChildWindowVisibilityChanged(Window* child,
@@ -106,6 +112,8 @@ void WorkspaceLayoutManager::OnChildWindowVisibilityChanged(Window* child,
     WindowPositioner::RearrangeVisibleWindowOnHideOrRemove(child);
   UpdateFullscreenState();
   UpdateShelfVisibility();
+  if (backdrop_delegate_)
+    backdrop_delegate_->OnChildWindowVisibilityChanged(child, visible);
 }
 
 void WorkspaceLayoutManager::SetChildBounds(
@@ -166,6 +174,8 @@ void WorkspaceLayoutManager::OnWindowPropertyChanged(Window* window,
 void WorkspaceLayoutManager::OnWindowStackingChanged(aura::Window* window) {
   UpdateShelfVisibility();
   UpdateFullscreenState();
+  if (backdrop_delegate_)
+    backdrop_delegate_->OnWindowStackingChanged(window);
 }
 
 void WorkspaceLayoutManager::OnWindowDestroying(aura::Window* window) {
@@ -214,6 +224,8 @@ void WorkspaceLayoutManager::OnPostWindowStateTypeChange(
   }
 
   UpdateShelfVisibility();
+  if (backdrop_delegate_)
+    backdrop_delegate_->OnPostWindowStateTypeChange(window_state, old_type);
 }
 
 //////////////////////////////////////////////////////////////////////////////
diff --git a/ash/wm/workspace/workspace_layout_manager.h b/ash/wm/workspace/workspace_layout_manager.h
index 6e2547a..ff15728 100644
--- a/ash/wm/workspace/workspace_layout_manager.h
+++ b/ash/wm/workspace/workspace_layout_manager.h
@@ -13,6 +13,7 @@
 #include "ash/wm/wm_types.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
+#include "base/memory/scoped_ptr.h"
 #include "ui/aura/client/activation_change_observer.h"
 #include "ui/aura/layout_manager.h"
 #include "ui/aura/window_observer.h"
@@ -36,6 +37,7 @@ class WMEvent;
 namespace internal {
 
 class ShelfLayoutManager;
+class WorkspaceLayoutManagerDelegate;
 
 // LayoutManager used on the window created for a workspace.
 class ASH_EXPORT WorkspaceLayoutManager
@@ -50,6 +52,12 @@ class ASH_EXPORT WorkspaceLayoutManager
 
   void SetShelf(internal::ShelfLayoutManager* shelf);
 
+  // A delegate which can be set to add a backdrop behind the top most visible
+  // window. With the call the ownership of the delegate will be transferred to
+  // the WorkspaceLayoutManager.
+  void SetMaximizeBackdropDelegate(
+      scoped_ptr<WorkspaceLayoutManagerDelegate> delegate);
+
   // Overridden from aura::LayoutManager:
   virtual void OnWindowResized() OVERRIDE {}
   virtual void OnWindowAddedToLayout(aura::Window* child) OVERRIDE;
@@ -103,6 +111,18 @@ class ASH_EXPORT WorkspaceLayoutManager
   // has changed.
   void UpdateFullscreenState();
 
+  // Updates the bounds of the window for a stte type change from
+  // |old_show_type|.
+  void UpdateBoundsFromStateType(wm::WindowState* window_state,
+                                 wm::WindowStateType old_state_type);
+
+  // If |window_state| is maximized or fullscreen the bounds of the
+  // window are set and true is returned. Does nothing otherwise.
+  bool SetMaximizedOrFullscreenBounds(wm::WindowState* window_state);
+
+  // Animates the window bounds to |bounds|.
+  void SetChildBoundsAnimated(aura::Window* child, const gfx::Rect& bounds);
+
   internal::ShelfLayoutManager* shelf_;
   aura::Window* window_;
   aura::Window* root_window_;
@@ -116,6 +136,10 @@ class ASH_EXPORT WorkspaceLayoutManager
   // True if this workspace is currently in fullscreen mode.
   bool is_fullscreen_;
 
+  // A window which covers the full container and which gets inserted behind the
+  // topmost visible window.
+  scoped_ptr<WorkspaceLayoutManagerDelegate> backdrop_delegate_;
+
   DISALLOW_COPY_AND_ASSIGN(WorkspaceLayoutManager);
 };
 
diff --git a/ash/wm/workspace/workspace_layout_manager_delegate.h b/ash/wm/workspace/workspace_layout_manager_delegate.h
new file mode 100644
index 0000000..a32c028
--- /dev/null
+++ b/ash/wm/workspace/workspace_layout_manager_delegate.h
@@ -0,0 +1,49 @@
+// 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.
+
+#ifndef ASH_WM_WORKSPACE_WORKSPACE_LAYOUT_MANAGER_DELEGATE_H_
+#define ASH_WM_WORKSPACE_WORKSPACE_LAYOUT_MANAGER_DELEGATE_H_
+
+#include "ash/wm/wm_types.h"
+
+namespace aura {
+class Window;
+}
+
+namespace ash {
+namespace wm {
+class WindowState;
+}
+
+namespace internal {
+
+// A delegate which can be set to create and control a backdrop which gets
+// placed below the top level window.
+class WorkspaceLayoutManagerDelegate {
+ public:
+  WorkspaceLayoutManagerDelegate() {}
+  virtual ~WorkspaceLayoutManagerDelegate() {}
+
+  // A window got added to the layout.
+  virtual void OnWindowAddedToLayout(aura::Window* child) = 0;
+
+  // A window got removed from the layout.
+  virtual void OnWindowRemovedFromLayout(aura::Window* child) = 0;
+
+  // The visibility of a window has changed.
+  virtual void OnChildWindowVisibilityChanged(aura::Window* child,
+                                              bool visible) = 0;
+
+  // The stacking order of a window has changed.
+  virtual void OnWindowStackingChanged(aura::Window* window) = 0;
+
+  // A window state type has changed.
+  virtual void OnPostWindowStateTypeChange(wm::WindowState* window_state,
+                                           wm::WindowStateType old_type) = 0;
+};
+
+}  // namespace internal
+}  // namespace ash
+
+#endif  // ASH_WM_WORKSPACE_WORKSPACE_LAYOUT_MANAGER_DELEGATE_H_
diff --git a/ash/wm/workspace/workspace_layout_manager_unittest.cc b/ash/wm/workspace/workspace_layout_manager_unittest.cc
index 77706e9..a27b484 100644
--- a/ash/wm/workspace/workspace_layout_manager_unittest.cc
+++ b/ash/wm/workspace/workspace_layout_manager_unittest.cc
@@ -14,6 +14,7 @@
 #include "ash/shell_observer.h"
 #include "ash/shell_window_ids.h"
 #include "ash/test/ash_test_base.h"
+#include "ash/wm/maximize_mode/workspace_backdrop_delegate.h"
 #include "ash/wm/window_state.h"
 #include "ash/wm/window_util.h"
 #include "ash/wm/wm_event.h"
@@ -774,4 +775,175 @@ TEST_F(WorkspaceLayoutManagerSoloTest, NotResizeWhenScreenIsLocked) {
   EXPECT_EQ(window_bounds.ToString(), window->bounds().ToString());
 }
 
+// Following tests are written to test the backdrop functionality.
+
+namespace {
+
+class WorkspaceLayoutManagerBackdropTest : public test::AshTestBase {
+ public:
+  WorkspaceLayoutManagerBackdropTest() {}
+  virtual ~WorkspaceLayoutManagerBackdropTest() {}
+
+  virtual void SetUp() OVERRIDE {
+    test::AshTestBase::SetUp();
+    UpdateDisplay("800x600");
+    default_container_ = Shell::GetContainer(
+        Shell::GetPrimaryRootWindow(),
+        internal::kShellWindowId_DefaultContainer);
+    // We set the size to something smaller then the display to avoid resizing
+    // issues with the shelf.
+    default_container_->SetBounds(gfx::Rect(0, 0, 800, 500));
+  }
+
+  aura::Window* CreateTestWindow(const gfx::Rect& bounds) {
+    aura::Window* window = CreateTestWindowInShellWithBounds(bounds);
+    return window;
+  }
+
+  // Turn the top window back drop on / off.
+  void ShowTopWindowBackdrop(bool show) {
+    scoped_ptr<ash::internal::WorkspaceLayoutManagerDelegate> backdrop;
+    if (show) {
+      backdrop.reset(new ash::internal::WorkspaceBackdropDelegate(
+          default_container_));
+    }
+    (static_cast<internal::WorkspaceLayoutManager*>
+        (default_container_->layout_manager()))->SetMaximizeBackdropDelegate(
+            backdrop.Pass());
+    // Closing and / or opening can be a delayed operation.
+    base::MessageLoop::current()->RunUntilIdle();
+  }
+
+  // Return the default container.
+  aura::Window* default_container() { return default_container_; }
+
+  // Return the order of windows (top most first) as they are in the default
+  // container. If the window is visible it will be a big letter, otherwise a
+  // small one. The backdrop will be an X and unknown windows will be shown as
+  // '!'.
+  std::string GetWindowOrderAsString(aura::Window* backdrop,
+                                     aura::Window* wa,
+                                     aura::Window* wb,
+                                     aura::Window* wc) {
+    std::string result;
+    for (int i = static_cast<int>(default_container()->children().size()) - 1;
+         i >= 0;
+         --i) {
+      if (!result.empty())
+        result += ",";
+      if (default_container()->children()[i] == wa)
+        result += default_container()->children()[i]->IsVisible() ? "A" : "a";
+      else if (default_container()->children()[i] == wb)
+        result += default_container()->children()[i]->IsVisible() ? "B" : "b";
+      else if (default_container()->children()[i] == wc)
+        result += default_container()->children()[i]->IsVisible() ? "C" : "c";
+      else if (default_container()->children()[i] == backdrop)
+        result += default_container()->children()[i]->IsVisible() ? "X" : "x";
+      else
+        result += "!";
+    }
+    return result;
+  }
+
+ private:
+  // The default container.
+  aura::Window* default_container_;
+
+  DISALLOW_COPY_AND_ASSIGN(WorkspaceLayoutManagerBackdropTest);
+};
+
+}  // namespace
+
+// Check that creating the BackDrop without destroying it does not lead into
+// a crash.
+TEST_F(WorkspaceLayoutManagerBackdropTest, BackdropCrashTest) {
+  ShowTopWindowBackdrop(true);
+}
+
+// Verify basic assumptions about the backdrop.
+TEST_F(WorkspaceLayoutManagerBackdropTest, BasicBackdropTests) {
+  // Create a backdrop and see that there is one window (the backdrop) and
+  // that the size is the same as the default container as well as that it is
+  // not visible.
+  ShowTopWindowBackdrop(true);
+  ASSERT_EQ(1U, default_container()->children().size());
+  EXPECT_FALSE(default_container()->children()[0]->IsVisible());
+
+  {
+    // Add a window and make sure that the backdrop is the second child.
+    scoped_ptr<aura::Window> window(CreateTestWindow(gfx::Rect(1, 2, 3, 4)));
+    window->Show();
+    ASSERT_EQ(2U, default_container()->children().size());
+    EXPECT_TRUE(default_container()->children()[0]->IsVisible());
+    EXPECT_TRUE(default_container()->children()[1]->IsVisible());
+    EXPECT_EQ(window.get(), default_container()->children()[1]);
+    EXPECT_EQ(default_container()->bounds().ToString(),
+              default_container()->children()[0]->bounds().ToString());
+  }
+
+  // With the window gone the backdrop should be invisible again.
+  ASSERT_EQ(1U, default_container()->children().size());
+  EXPECT_FALSE(default_container()->children()[0]->IsVisible());
+
+  // Destroying the Backdrop should empty the container.
+  ShowTopWindowBackdrop(false);
+  ASSERT_EQ(0U, default_container()->children().size());
+}
+
+// Verify that the backdrop gets properly created and placed.
+TEST_F(WorkspaceLayoutManagerBackdropTest, VerifyBackdropAndItsStacking) {
+  scoped_ptr<aura::Window> window1(CreateTestWindow(gfx::Rect(1, 2, 3, 4)));
+  window1->Show();
+
+  // Get the default container and check that only a single window is in there.
+  ASSERT_EQ(1U, default_container()->children().size());
+  EXPECT_EQ(window1.get(), default_container()->children()[0]);
+  EXPECT_EQ("A", GetWindowOrderAsString(NULL, window1.get(), NULL, NULL));
+
+  // Create 2 more windows and check that they are also in the container.
+  scoped_ptr<aura::Window> window2(CreateTestWindow(gfx::Rect(10, 2, 3, 4)));
+  scoped_ptr<aura::Window> window3(CreateTestWindow(gfx::Rect(20, 2, 3, 4)));
+  window2->Show();
+  window3->Show();
+
+  aura::Window* backdrop = NULL;
+  EXPECT_EQ("C,B,A",
+            GetWindowOrderAsString(backdrop, window1.get(), window2.get(),
+                                   window3.get()));
+
+  // Turn on the backdrop mode and check that the window shows up where it
+  // should be (second highest number).
+  ShowTopWindowBackdrop(true);
+  backdrop = default_container()->children()[2];
+  EXPECT_EQ("C,X,B,A",
+            GetWindowOrderAsString(backdrop, window1.get(), window2.get(),
+                                   window3.get()));
+
+  // Switch the order of windows and check that it still remains in that
+  // location.
+  default_container()->StackChildAtTop(window2.get());
+  EXPECT_EQ("B,X,C,A",
+            GetWindowOrderAsString(backdrop, window1.get(), window2.get(),
+                                   window3.get()));
+
+  // Make the top window invisible and check.
+  window2.get()->Hide();
+  EXPECT_EQ("b,C,X,A",
+            GetWindowOrderAsString(backdrop, window1.get(), window2.get(),
+                                   window3.get()));
+  // Then delete window after window and see that everything is in order.
+  window1.reset();
+  EXPECT_EQ("b,C,X",
+            GetWindowOrderAsString(backdrop, window1.get(), window2.get(),
+                                   window3.get()));
+  window3.reset();
+  EXPECT_EQ("b,x",
+            GetWindowOrderAsString(backdrop, window1.get(), window2.get(),
+                                   window3.get()));
+  ShowTopWindowBackdrop(false);
+  EXPECT_EQ("b",
+            GetWindowOrderAsString(NULL, window1.get(), window2.get(),
+                                   window3.get()));
+}
+
 }  // namespace ash
diff --git a/ash/wm/workspace_controller.cc b/ash/wm/workspace_controller.cc
index 55ccf64..9b9f35e 100644
--- a/ash/wm/workspace_controller.cc
+++ b/ash/wm/workspace_controller.cc
@@ -13,6 +13,7 @@
 #include "ash/wm/window_util.h"
 #include "ash/wm/workspace/workspace_event_handler.h"
 #include "ash/wm/workspace/workspace_layout_manager.h"
+#include "ash/wm/workspace/workspace_layout_manager_delegate.h"
 #include "ui/aura/client/activation_client.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/window.h"
@@ -135,5 +136,10 @@ void WorkspaceController::DoInitialAnimation() {
   }
 }
 
+void WorkspaceController::SetMaximizeBackdropDelegate(
+    scoped_ptr<WorkspaceLayoutManagerDelegate> delegate) {
+  layout_manager_->SetMaximizeBackdropDelegate(delegate.Pass());
+}
+
 }  // namespace internal
 }  // namespace ash
diff --git a/ash/wm/workspace_controller.h b/ash/wm/workspace_controller.h
index 84df41c..175ebe7 100644
--- a/ash/wm/workspace_controller.h
+++ b/ash/wm/workspace_controller.h
@@ -21,6 +21,7 @@ class ShelfLayoutManager;
 class WorkspaceControllerTestHelper;
 class WorkspaceEventHandler;
 class WorkspaceLayoutManager;
+class WorkspaceLayoutManagerDelegate;
 
 // WorkspaceController acts as a central place that ties together all the
 // various workspace pieces.
@@ -37,6 +38,11 @@ class ASH_EXPORT WorkspaceController {
   // Starts the animation that occurs on first login.
   void DoInitialAnimation();
 
+  // Add a delegate which adds a backdrop behind the top window of the default
+  // workspace.
+  void SetMaximizeBackdropDelegate(
+      scoped_ptr<WorkspaceLayoutManagerDelegate> delegate);
+
  private:
   friend class WorkspaceControllerTestHelper;