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

ash/wm/workspace/workspace_layout_manager.h

Index: ash/wm/workspace/workspace_layout_manager.h
diff --git a/ash/wm/workspace/workspace_layout_manager.h b/ash/wm/workspace/workspace_layout_manager.h
index e1781b849c71d63baa30ff332177d752f27dad0c..e813c3f567668e5b311bc430b47f212a2efec528 100644
--- a/ash/wm/workspace/workspace_layout_manager.h
+++ b/ash/wm/workspace/workspace_layout_manager.h
@@ -55,6 +55,7 @@ class ASH_EXPORT WorkspaceLayoutManager : public BaseLayoutManager {
   virtual void OnWindowPropertyChanged(aura::Window* window,
                                        const void* key,
                                        intptr_t old) OVERRIDE;
+  virtual void OnWindowStackingChanged(aura::Window* window) OVERRIDE;
 
   // ash::WindowSettings::Observer overrides:
   virtual void OnTrackedByWorkspaceChanged(wm::WindowState* window_state,
@@ -77,6 +78,7 @@ class ASH_EXPORT WorkspaceLayoutManager : public BaseLayoutManager {
   void AdjustWindowBoundsWhenAdded(wm::WindowState* window_state);
 
   void UpdateDesktopVisibility();
+  void UpdateFullscreenState();
 
   // Updates the bounds of the window for a show state change from
   // |last_show_state|.
@@ -101,6 +103,9 @@ class ASH_EXPORT WorkspaceLayoutManager : public BaseLayoutManager {
   // workspace switch.
   gfx::Rect work_area_in_parent_;
 
+  // True if this workspace is currently in fullscreen mode.
+  bool is_fullscreen_;
+
   DISALLOW_COPY_AND_ASSIGN(WorkspaceLayoutManager);
 };