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

ash/wm/maximize_mode/maximize_mode_window_manager.cc

Index: ash/wm/maximize_mode/maximize_mode_window_manager.cc
diff --git a/ash/wm/maximize_mode/maximize_mode_window_manager.cc b/ash/wm/maximize_mode/maximize_mode_window_manager.cc
index 6360450d36cbd9f62e045c0f8147dd037646d6a2..feb668c6da1e71789d562768bda73f850eabae78 100644
--- a/ash/wm/maximize_mode/maximize_mode_window_manager.cc
+++ b/ash/wm/maximize_mode/maximize_mode_window_manager.cc
@@ -4,9 +4,11 @@
 
 #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/wm/mru_window_tracker.h"
+#include "ash/wm/workspace_controller.h"
 #include "ui/aura/window.h"
 #include "ui/gfx/screen.h"
 
@@ -14,7 +16,9 @@ namespace ash {
 namespace internal {
 
 MaximizeModeWindowManager::~MaximizeModeWindowManager() {
+  Shell::GetInstance()->RemoveShellObserver(this);
   Shell::GetScreen()->RemoveObserver(this);
+  EnableBackdropBehindTopWindowOnEachDisplay(false);
   RemoveWindowCreationObservers();
   RestoreAllWindows();
 }
@@ -23,6 +27,22 @@ int MaximizeModeWindowManager::GetNumberOfManagedWindows() {
   return initial_show_state_.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))
@@ -58,25 +78,28 @@ void MaximizeModeWindowManager::OnDisplayBoundsChanged(
 }
 
 void MaximizeModeWindowManager::OnDisplayAdded(const gfx::Display& display) {
-  RemoveWindowCreationObservers();
-  AddWindowCreationObservers();
-
+  DisplayConfigurationChanged();
 }
+
 void MaximizeModeWindowManager::OnDisplayRemoved(const gfx::Display& display) {
-  RemoveWindowCreationObservers();
-  AddWindowCreationObservers();
+  DisplayConfigurationChanged();
 }
 
-MaximizeModeWindowManager::MaximizeModeWindowManager() {
+MaximizeModeWindowManager::MaximizeModeWindowManager()
+      : backdrops_hidden_(false) {
   MaximizeAllWindows();
   AddWindowCreationObservers();
+  EnableBackdropBehindTopWindowOnEachDisplay(true);
   Shell::GetScreen()->AddObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
 }
 
 void MaximizeModeWindowManager::MaximizeAllWindows() {
   MruWindowTracker::WindowList windows =
       MruWindowTracker::BuildWindowList(false);
   // Add all existing Mru windows.
+  // TODO(skuhne): The MRUWindowTracker also includes always on top and panel
+  // windows. Panel windows shouldn't be a problem, but always on top might be.
   for (MruWindowTracker::WindowList::iterator window = windows.begin();
       window != windows.end(); ++window) {
     MaximizeAndTrackWindow(*window);
@@ -116,7 +139,6 @@ 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 != ui::SHOW_STATE_MINIMIZED)
@@ -131,7 +153,6 @@ void MaximizeModeWindowManager::RestoreAndForgetWindow(
   // Restore window if it can be restored.
   if (state != ui::SHOW_STATE_MAXIMIZED) {
     if (!CanMaximize(window)) {
-      // TODO(skuhne): Remove the background cover layer.
       ash::wm::WindowState* window_state = ash::wm::GetWindowState(window);
       DCHECK(window_state->HasRestoreBounds());
       gfx::Rect initial_bounds =
@@ -193,6 +214,7 @@ void MaximizeModeWindowManager::AddWindowCreationObservers() {
   aura::Window::Windows root_windows = Shell::GetAllRootWindows();
   for (aura::Window::Windows::const_iterator iter = root_windows.begin();
        iter != root_windows.end(); ++iter) {
+    // TODO(skuhne): We might only need the DefaultContainer here.
     for (size_t i = 0; i < kSwitchableWindowContainerIdsLength; ++i) {
       aura::Window* container = Shell::GetContainer(*iter,
           kSwitchableWindowContainerIds[i]);
@@ -213,10 +235,32 @@ void MaximizeModeWindowManager::RemoveWindowCreationObservers() {
   observed_container_windows_.clear();
 }
 
+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;
+    controller->workspace_controller()->AddBackdropBehindTopWindow(enable);
+  }
+}
+
 bool MaximizeModeWindowManager::IsContainerWindow(aura::Window* window) {
   return observed_container_windows_.find(window) !=
              observed_container_windows_.end();
 }
 
+void MaximizeModeWindowManager::DisplayConfigurationChanged() {
+  EnableBackdropBehindTopWindowOnEachDisplay(false);
+  RemoveWindowCreationObservers();
+  AddWindowCreationObservers();
+  EnableBackdropBehindTopWindowOnEachDisplay(true);
+}
+
 }  // namespace internal
 }  // namespace ash