Sets the background color of shelf is opaque black when maximized (2nd)

ash/shelf/shelf_types.h

Index: ash/shelf/shelf_types.h
diff --git a/ash/shelf/shelf_types.h b/ash/shelf/shelf_types.h
index 82cf63050c53ae2e85cc05f3cf61638889d30649..4ee3b94c09a94a373efb59163d8aed64c0351adf 100644
--- a/ash/shelf/shelf_types.h
+++ b/ash/shelf/shelf_types.h
@@ -41,6 +41,17 @@ enum ShelfAutoHideState {
   SHELF_AUTO_HIDE_HIDDEN,
 };
 
+enum ShelfBackgroundType {
+  // The default transparent background.
+  SHELF_BACKGROUND_DEFAULT,
+
+  // The background when a window is overlapping.
+  SHELF_BACKGROUND_OVERLAP,
+
+  // The background when a window is maximized.
+  SHELF_BACKGROUND_MAXIMIZED,
+};
+
 }  // namespace ash
 
 #endif  // ASH_SHELF_SHELF_TYPES_H_