chromeos: Remove some WmWindow usage from ash/system

ash/system/ime_menu/ime_menu_tray.cc

Index: ash/system/ime_menu/ime_menu_tray.cc
diff --git a/ash/system/ime_menu/ime_menu_tray.cc b/ash/system/ime_menu/ime_menu_tray.cc
index e75c7e0e1f57862a6b2f054d57ecbc1234bcd92a..94229ff9b9e56b61dec116ad965049013e4785b8 100644
--- a/ash/system/ime_menu/ime_menu_tray.cc
+++ b/ash/system/ime_menu/ime_menu_tray.cc
@@ -24,7 +24,6 @@
 #include "ash/system/tray/tray_popup_item_style.h"
 #include "ash/system/tray/tray_popup_utils.h"
 #include "ash/system/tray/tray_utils.h"
-#include "ash/wm_window.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/utf_string_conversions.h"
 #include "components/session_manager/session_manager_types.h"
@@ -476,8 +475,7 @@ void ImeMenuTray::OnBeforeBubbleWidgetInit(
     views::Widget* bubble_widget,
     views::Widget::InitParams* params) const {
   // Place the bubble in the same root window as |anchor_widget|.
-  WmWindow::Get(anchor_widget->GetNativeWindow())
-      ->GetRootWindowController()
+  RootWindowController::ForWindow(anchor_widget->GetNativeWindow())
       ->ConfigureWidgetInitParamsForContainer(
           bubble_widget, kShellWindowId_SettingBubbleContainer, params);
 }