RootWindowController::GetFullscreenWindow() should return the active one.

ash/root_window_controller.h

Index: ash/root_window_controller.h
diff --git a/ash/root_window_controller.h b/ash/root_window_controller.h
index d57aaf8a1bd97b8bc746478a21b84ea161920551..211cf0c8fa847a38c7a55b912158ad8fbb37e2cb 100644
--- a/ash/root_window_controller.h
+++ b/ash/root_window_controller.h
@@ -206,10 +206,9 @@ class ASH_EXPORT RootWindowController : public ShellObserver {
   // Initialize touch HUDs if necessary.
   void InitTouchHuds();
 
-  // Returns the window, if any, which is in fullscreen mode in the active
-  // workspace. Exposed here so clients of Ash don't need to know the details
-  // of workspace management.
-  const aura::Window* GetFullscreenWindow() const;
+  // Returns the window, if any, which is in fullscreen mode. If multiple
+  // windows are in fullscreen state, the topmost one is preferred.
+  const aura::Window* GetTopmostFullscreenWindow() const;
 
  private:
   void InitLayoutManagers();