Ignore fullscreen windows which are behind other windows for fullscreen mode.

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 a791db5b055c101253a64c3f1b541b18cc45162c..4a8a60da7acb08c9e4e2d0125b2419856356ff11 100644
--- a/ash/wm/workspace/workspace_layout_manager.cc
+++ b/ash/wm/workspace/workspace_layout_manager.cc
@@ -170,6 +170,12 @@ void WorkspaceLayoutManager::OnTrackedByWorkspaceChanged(
   }
 }
 
+void WorkspaceLayoutManager::OnWindowActivated(aura::Window* gained_active,
+                                               aura::Window* lost_active) {
+  BaseLayoutManager::OnWindowActivated(gained_active, lost_active);
+  UpdateDesktopVisibility();
+}
+
 void WorkspaceLayoutManager::OnWindowShowTypeChanged(
     wm::WindowState* window_state,
     wm::WindowShowType old_type) {