Mash: Show app icons in shelf based on the Widget's app icon

ash/mus/shelf_delegate_mus.h

Index: ash/mus/shelf_delegate_mus.h
diff --git a/ash/mus/shelf_delegate_mus.h b/ash/mus/shelf_delegate_mus.h
index 47364fce7e8b9bfaa66f31ce7ed152de50c2a30e..333a84dc54547218e8c91f74323e9850670f196c 100644
--- a/ash/mus/shelf_delegate_mus.h
+++ b/ash/mus/shelf_delegate_mus.h
@@ -41,6 +41,8 @@ class ShelfDelegateMus : public ShelfDelegate,
   void OnUserWindowRemoved(uint32_t window_id) override;
   void OnUserWindowTitleChanged(uint32_t window_id,
                                 const mojo::String& window_title) override;
+  void OnUserWindowAppIconChanged(uint32_t window_id,
+                                  mojo::Array<uint8_t> app_icon) override;
   void OnUserWindowFocusChanged(uint32_t window_id, bool has_focus) override;
 
   ShelfModel* model_;