Simplify layout of tray items and fix spacing for MD.

ash/common/system/tray/tray_image_item.h

Index: ash/common/system/tray/tray_image_item.h
diff --git a/ash/common/system/tray/tray_image_item.h b/ash/common/system/tray/tray_image_item.h
index 41413e5d795ab282c55e2d45469683a61cf6be4c..db4c3f0b654dc074f172cc7b36e0c815c82dc607 100644
--- a/ash/common/system/tray/tray_image_item.h
+++ b/ash/common/system/tray/tray_image_item.h
@@ -46,9 +46,6 @@ class ASH_EXPORT TrayImageItem : public SystemTrayItem {
   void SetImageFromResourceId(int resource_id);
 
  private:
-  // Set the alignment of the image depending on the shelf alignment.
-  void SetItemAlignment(ShelfAlignment alignment);
-
   // Sets the current icon on |tray_view_|'s ImageView.
   void UpdateImageOnImageView();