Revert of Refactor backdrop

ash/wm/maximize_mode/maximize_mode_window_manager.h

Index: ash/wm/maximize_mode/maximize_mode_window_manager.h
diff --git a/ash/wm/maximize_mode/maximize_mode_window_manager.h b/ash/wm/maximize_mode/maximize_mode_window_manager.h
index 6641b247b0a835e931096f5f23c449f3010a40bb..4caa571d50098e8746aa9f275108f1f003a222fc 100644
--- a/ash/wm/maximize_mode/maximize_mode_window_manager.h
+++ b/ash/wm/maximize_mode/maximize_mode_window_manager.h
@@ -131,6 +131,9 @@
   // Windows added to the container, but not yet shown.
   std::unordered_set<aura::Window*> added_windows_;
 
+  // True if all backdrops are hidden.
+  bool backdrops_hidden_;
+
   std::unique_ptr<wm::MaximizeModeEventHandler> event_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(MaximizeModeWindowManager);