chromeos: Make system tray audio item observe CrasAudioHandler directly

ash/common/wm_root_window_controller.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/common/wm_root_window_controller.h"
 
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/shelf/shelf_layout_manager.h"
 #include "ash/common/shelf/shelf_widget.h"
 #include "ash/common/shelf/wm_shelf.h"
@@ skipping 206 matching lines @@
 
 void WmRootWindowController::ShowShelf() {
   WmShelf* shelf = GetShelf();
   if (!shelf->IsShelfInitialized())
     return;
   // TODO(jamescook): Move this into WmShelf.
   shelf->shelf_widget()->SetShelfVisibility(true);
   shelf->shelf_widget()->status_area_widget()->Show();
 }
 
+SystemTray* WmRootWindowController::GetSystemTray() {
+  ShelfWidget* shelf_widget = GetShelf()->shelf_widget();
+  if (!shelf_widget || !shelf_widget->status_area_widget())
+    return nullptr;
+  return shelf_widget->status_area_widget()->system_tray();
+}
+
 WmWindow* WmRootWindowController::GetContainer(int container_id) {
   return root_->GetChildByShellWindowId(container_id);
 }
 
 const WmWindow* WmRootWindowController::GetContainer(int container_id) const {
   return root_->GetChildByShellWindowId(container_id);
 }
 
 void WmRootWindowController::ShowContextMenu(
     const gfx::Point& location_in_screen,
@@ skipping 350 matching lines @@
 }
 
 void WmRootWindowController::OnMenuClosed() {
   menu_runner_.reset();
   menu_model_adapter_.reset();
   menu_model_.reset();
   GetShelf()->UpdateVisibilityState();
 }
 
 }  // namespace ash