chromeos: Make system tray audio item observe CrasAudioHandler directly

ash/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 import("//ui/base/ui_features.gni")
 
 assert(use_aura)
@@ skipping 173 matching lines @@
     "common/shelf/wm_shelf.cc",
     "common/shelf/wm_shelf.h",
     "common/shelf/wm_shelf_observer.h",
     "common/shelf/wm_shelf_util.cc",
     "common/shelf/wm_shelf_util.h",
     "common/shell_delegate.h",
     "common/system/accessibility_observer.h",
     "common/system/brightness_control_delegate.h",
     "common/system/chromeos/audio/audio_detailed_view.cc",
     "common/system/chromeos/audio/audio_detailed_view.h",
-    "common/system/chromeos/audio/audio_observer.h",
     "common/system/chromeos/audio/tray_audio.cc",
     "common/system/chromeos/audio/tray_audio.h",
     "common/system/chromeos/audio/tray_audio_delegate.h",
     "common/system/chromeos/audio/tray_audio_delegate_chromeos.cc",
     "common/system/chromeos/audio/tray_audio_delegate_chromeos.h",
     "common/system/chromeos/audio/volume_view.cc",
     "common/system/chromeos/audio/volume_view.h",
     "common/system/chromeos/bluetooth/bluetooth_notification_controller.cc",
     "common/system/chromeos/bluetooth/bluetooth_notification_controller.h",
     "common/system/chromeos/bluetooth/bluetooth_observer.h",
@@ skipping 1286 matching lines @@
   if (is_win) {
     configs -= [ "//build/config/win:console" ]
     configs += [ "//build/config/win:windowed" ]
     deps += [ "//sandbox" ]
   }
 
   if (is_chromeos) {
     deps += [ "//device/bluetooth" ]
   }
 }