Use MD-ash's auto hide behavior for arc++ windows.

ash/shelf/shelf_layout_manager.h

Index: ash/shelf/shelf_layout_manager.h
diff --git a/ash/shelf/shelf_layout_manager.h b/ash/shelf/shelf_layout_manager.h
index b28a16e76883596720aaaf8100497267a87ba6ac..8bc668b225530f1610e6a32e0d7df4fd2dfe94d2 100644
--- a/ash/shelf/shelf_layout_manager.h
+++ b/ash/shelf/shelf_layout_manager.h
@@ -14,6 +14,7 @@
 #include "ash/common/wm/background_animator.h"
 #include "ash/common/wm/dock/docked_window_layout_manager_observer.h"
 #include "ash/common/wm/lock_state_observer.h"
+#include "ash/common/wm/window_state.h"
 #include "ash/common/wm/wm_snap_to_pixel_layout_manager.h"
 #include "ash/common/wm/workspace/workspace_types.h"
 #include "ash/common/wm_activation_observer.h"
@@ -291,6 +292,7 @@ class ASH_EXPORT ShelfLayoutManager
   // Returns true if there is a fullscreen window open that causes the shelf
   // to be hidden.
   bool IsShelfHiddenForFullscreen() const;
+  ash::wm::WindowState::FullscreenShelfMode GetShelfModeForFullscreen() const;
 
   // Gesture related functions:
   void StartGestureDrag(const ui::GestureEvent& gesture);
@@ -298,6 +300,8 @@ class ASH_EXPORT ShelfLayoutManager
   void CompleteGestureDrag(const ui::GestureEvent& gesture);
   void CancelGestureDrag();
 
+  int GetShelfInsetsForAutoHide() const;
+
   // True when inside UpdateBoundsAndOpacity() method. Used to prevent calling
   // UpdateBoundsAndOpacity() again from SetChildBounds().
   bool updating_bounds_;
@@ -362,6 +366,10 @@ class ASH_EXPORT ShelfLayoutManager
   // The show hide animation duration override or 0 for default.
   int duration_override_in_ms_;
 
+  // The flag to enforce invisible shelf (as in MD-experiemntal).
+  // TODO(oshima): Remove this when MD immersive is launched.
+  bool invisible_auto_hide_shelf_ = false;
+
   std::unique_ptr<RootWindowControllerObserverImpl>
       root_window_controller_observer_;