Create a LayerDelegate for recreated layers to draw when their content is invalidated.

ash/wm/drag_window_controller.h

Index: ash/wm/drag_window_controller.h
diff --git a/ash/wm/drag_window_controller.h b/ash/wm/drag_window_controller.h
index 27225f01f348df86db51d50c48d9d1dbd61de52b..373cb0c901ebfe62c92452eab58965cebcc99a0d 100644
--- a/ash/wm/drag_window_controller.h
+++ b/ash/wm/drag_window_controller.h
@@ -41,6 +41,12 @@ class ASH_EXPORT DragWindowController {
   void Update(const gfx::Rect& bounds_in_screen,
               const gfx::Point& drag_location_in_screen);
 
+ private:
+  class DragWindowDetails;
+  FRIEND_TEST_ALL_PREFIXES(DragWindowResizerTest, DragWindowController);
+  FRIEND_TEST_ALL_PREFIXES(DragWindowResizerTest,
+                           DragWindowControllerAcrossThreeDisplays);
+
   // Returns the currently active drag windows.
   int GetDragWindowsCountForTest() const;
 
@@ -49,8 +55,8 @@ class ASH_EXPORT DragWindowController {
   const aura::Window* GetDragWindowForTest(size_t index) const;
   const ui::LayerTreeOwner* GetDragLayerOwnerForTest(size_t index) const;
 
- private:
-  class DragWindowDetails;
+  // Call Layer::OnPaintLayer on all layers under the drag_windows_.
+  void RequestLayerPaintForTest();
 
   // Window the drag window is placed beneath.
   aura::Window* window_;