ash: Remove aura dependencies from ash/system/web_notification

ash/shelf/shelf.cc

Index: ash/shelf/shelf.cc
diff --git a/ash/shelf/shelf.cc b/ash/shelf/shelf.cc
index 9009532e78731200b901ae9bf77dd81e0a4e41dd..35bf021510c1a509300d30777b2fb27669aab40b 100644
--- a/ash/shelf/shelf.cc
+++ b/ash/shelf/shelf.cc
@@ -11,6 +11,7 @@
 #include "ash/common/wm/shelf/wm_shelf_util.h"
 #include "ash/focus_cycler.h"
 #include "ash/root_window_controller.h"
+#include "ash/root_window_settings.h"
 #include "ash/screen_util.h"
 #include "ash/shelf/shelf_delegate.h"
 #include "ash/shelf/shelf_item_delegate.h"
@@ -72,6 +73,18 @@ Shelf* Shelf::ForWindow(const aura::Window* window) {
   return shelf_widget ? shelf_widget->shelf() : nullptr;
 }
 
+// static
+Shelf* Shelf::ForDisplayId(int64_t display_id) {
+  for (aura::Window* window : Shell::GetInstance()->GetAllRootWindows()) {
+    RootWindowSettings* settings = GetRootWindowSettings(window);
+    if (settings->display_id == display_id && settings->controller) {
+      ShelfWidget* shelf_widget = settings->controller->shelf_widget();
+      return shelf_widget ? shelf_widget->shelf() : nullptr;
+    }
+  }
+  return nullptr;
+}
+
 void Shelf::SetAlignment(wm::ShelfAlignment alignment) {
   if (alignment_ == alignment)
     return;