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

ash/wm/workspace/workspace_layout_manager.cc

Index: ash/wm/workspace/workspace_layout_manager.cc
diff --git a/ash/wm/workspace/workspace_layout_manager.cc b/ash/wm/workspace/workspace_layout_manager.cc
index a5ca0a08b7dfbcd4204b39b0b8d4e26d203bc277..d6118ea851469d6f3996dcffbbf107df15965606 100644
--- a/ash/wm/workspace/workspace_layout_manager.cc
+++ b/ash/wm/workspace/workspace_layout_manager.cc
@@ -16,6 +16,7 @@
 #include "ash/wm/window_properties.h"
 #include "ash/wm/window_state.h"
 #include "ash/wm/window_util.h"
+#include "ash/wm/workspace/workspace_layout_manager_backdrop.h"
 #include "ui/aura/client/activation_client.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/window.h"
@@ -59,6 +60,15 @@ void WorkspaceLayoutManager::SetShelf(internal::ShelfLayoutManager* shelf) {
   shelf_ = shelf;
 }
 
+void WorkspaceLayoutManager::AddBackdropBehindTopWindow(bool enable) {
+  if ((NULL != backdrop_.get()) == enable)

[sky, 2014/03/06 01:03:18]

nit: creating a local variable for NULL != backdrop_.get() is a lot more
readable.

[Mr4D (OOO till 08-26), 2014/03/06 17:17:16]

Done.

+    return;
+  if (enable)
+    backdrop_.reset(new WorkspaceLayoutManagerBackdrop(window_));
+  else
+    backdrop_.reset();
+}
+
 //////////////////////////////////////////////////////////////////////////////
 // WorkspaceLayoutManager, aura::LayoutManager implementation:
 
@@ -70,6 +80,7 @@ void WorkspaceLayoutManager::OnWindowAddedToLayout(Window* child) {
   window_state->AddObserver(this);
   UpdateShelfVisibility();
   UpdateFullscreenState();
+  UpdateStackingAndVisibilityOfBackdrop();

[sky, 2014/03/06 01:03:18]

How about a delegate method that is called at all these places? That way
WorskpaceLayoutManager does't have to own the backdrop_ or know anything about
it.

[Mr4D (OOO till 08-26), 2014/03/06 17:17:16]

Done.

   WindowPositioner::RearrangeVisibleWindowOnShow(child);
 }
 
@@ -85,6 +96,7 @@ void WorkspaceLayoutManager::OnWillRemoveWindowFromLayout(Window* child) {
 void WorkspaceLayoutManager::OnWindowRemovedFromLayout(Window* child) {
   UpdateShelfVisibility();
   UpdateFullscreenState();
+  UpdateStackingAndVisibilityOfBackdrop();
 }
 
 void WorkspaceLayoutManager::OnChildWindowVisibilityChanged(Window* child,
@@ -102,6 +114,7 @@ void WorkspaceLayoutManager::OnChildWindowVisibilityChanged(Window* child,
     WindowPositioner::RearrangeVisibleWindowOnHideOrRemove(child);
   }
   UpdateShelfVisibility();
+  UpdateStackingAndVisibilityOfBackdrop();
 }
 
 void WorkspaceLayoutManager::SetChildBounds(
@@ -139,6 +152,7 @@ void WorkspaceLayoutManager::OnWindowPropertyChanged(Window* window,
 void WorkspaceLayoutManager::OnWindowStackingChanged(aura::Window* window) {
   UpdateShelfVisibility();
   UpdateFullscreenState();
+  UpdateStackingAndVisibilityOfBackdrop();
 }
 
 void WorkspaceLayoutManager::OnWindowDestroying(aura::Window* window) {
@@ -181,6 +195,7 @@ void WorkspaceLayoutManager::OnPostWindowShowTypeChange(
     UpdateFullscreenState();
 
   UpdateShelfVisibility();
+  UpdateStackingAndVisibilityOfBackdrop();
 }
 
 //////////////////////////////////////////////////////////////////////////////
@@ -219,6 +234,11 @@ void WorkspaceLayoutManager::UpdateShelfVisibility() {
     shelf_->UpdateVisibilityState();
 }
 
+void WorkspaceLayoutManager::UpdateStackingAndVisibilityOfBackdrop() {
+  if (backdrop_)
+    backdrop_->RestackOrHideWindow();
+}
+
 void WorkspaceLayoutManager::UpdateFullscreenState() {
   bool is_fullscreen = GetRootWindowController(
       window_->GetRootWindow())->GetWindowForFullscreenMode() != NULL;