Handle app custom icon via aura::Window property.

extensions/browser/app_window/app_window_registry.cc

Index: extensions/browser/app_window/app_window_registry.cc
diff --git a/extensions/browser/app_window/app_window_registry.cc b/extensions/browser/app_window/app_window_registry.cc
index 3eb52cabfdc75a73c06d6540beee28e5ab1db9b7..bd259b0ba1e150c6e31efebe26762f7bd88747a7 100644
--- a/extensions/browser/app_window/app_window_registry.cc
+++ b/extensions/browser/app_window/app_window_registry.cc
@@ -24,10 +24,6 @@ namespace extensions {
 void AppWindowRegistry::Observer::OnAppWindowAdded(AppWindow* app_window) {
 }
 
-void AppWindowRegistry::Observer::OnAppWindowIconChanged(
-    AppWindow* app_window) {
-}
-
 void AppWindowRegistry::Observer::OnAppWindowRemoved(AppWindow* app_window) {
 }
 
@@ -64,12 +60,6 @@ void AppWindowRegistry::AddAppWindow(AppWindow* app_window) {
     observer.OnAppWindowAdded(app_window);
 }
 
-void AppWindowRegistry::AppWindowIconChanged(AppWindow* app_window) {
-  AddAppWindowToList(app_window);
-  for (auto& observer : observers_)
-    observer.OnAppWindowIconChanged(app_window);
-}
-
 void AppWindowRegistry::AppWindowActivated(AppWindow* app_window) {
   BringToFront(app_window);
   for (auto& observer : observers_)