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

mash/wm/public/interfaces/user_window_controller.mojom

Index: mash/wm/public/interfaces/user_window_controller.mojom
diff --git a/mash/wm/public/interfaces/user_window_controller.mojom b/mash/wm/public/interfaces/user_window_controller.mojom
index c1d61d8a355b3d52cfcf7bb6445b734ff0b64dc9..3d84fb11d06376c484484524f6ca499df7c2374e 100644
--- a/mash/wm/public/interfaces/user_window_controller.mojom
+++ b/mash/wm/public/interfaces/user_window_controller.mojom
@@ -8,6 +8,7 @@ struct UserWindow {
   uint32 window_id;
   string window_title;
   bool window_has_focus;
+  array<uint8> window_app_icon;  // Serialized SkBitmap.
 };
 
 // An observer of user windows within mojom::Container::USER_WINDOWS.
@@ -20,6 +21,9 @@ interface UserWindowObserver {
   OnUserWindowRemoved(uint32 window_id);
 
   OnUserWindowTitleChanged(uint32 window_id, string window_title);
+  
+  // |app_icon| is a serialized SkBitmap.
+  OnUserWindowAppIconChanged(uint32 window_id, array<uint8> app_icon);
 
   OnUserWindowFocusChanged(uint32 window_id, bool has_focus);
 };