Support for showing/hiding status area volume controls in desktop devices

chrome/browser/chromeos/status/volume_menu_button.cc

 // Copyright (c) 2012 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 "chrome/browser/chromeos/status/volume_menu_button.h"
 
 #include <algorithm>
 
 #include "base/string_number_conversions.h"
 #include "chrome/browser/chromeos/audio/audio_handler.h"
 #include "chrome/browser/chromeos/status/status_area_bubble.h"
+#include "chrome/browser/chromeos/system/runtime_environment.h"
 #include "chrome/browser/chromeos/view_ids.h"
 #include "grit/generated_resources.h"
 #include "grit/theme_resources.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/canvas_skia.h"
 #include "ui/gfx/image/image.h"
 #include "ui/views/controls/menu/menu_item_view.h"
 #include "ui/views/controls/menu/menu_runner.h"
@@ skipping 143 matching lines @@
 
 namespace chromeos {
 
 ////////////////////////////////////////////////////////////////////////////////
 // VolumeMenuButton
 
 VolumeMenuButton::VolumeMenuButton(StatusAreaButton::Delegate* delegate)
     : StatusAreaButton(delegate, this) {
   set_id(VIEW_ID_STATUS_BUTTON_VOLUME);
   UpdateIcon();
-  // TODO(achuith): Query SystemKeyEventListener to determine when we
-  // can show statusbar volume controls.
-  SetVisible(false);
+
+  DCHECK(SystemKeyEventListener::GetInstance() ||
+         !system::runtime_environment::IsRunningOnChromeOS());
+  if (SystemKeyEventListener::GetInstance())
+    SystemKeyEventListener::GetInstance()->AddStatusAreaVolumeObserver(this);
 }
 
 VolumeMenuButton::~VolumeMenuButton() {
+  if (SystemKeyEventListener::GetInstance())
+    SystemKeyEventListener::GetInstance()->RemoveStatusAreaVolumeObserver(this);
 }
 
 int VolumeMenuButton::icon_width() {
   return kVolumeIconWidth;
 }
 
 void VolumeMenuButton::UpdateIcon() {
   const int volume_percent = GetVolumePercent();
   string16 tooltip_text = (volume_percent == 0)
       ? l10n_util::GetStringUTF16(IDS_STATUSBAR_VOLUME_MUTE)
@@ skipping 35 matching lines @@
       source->GetWidget()->GetTopLevelWidget(),
       this,
       bounds,
       views::MenuItemView::TOPRIGHT,
       views::MenuRunner::HAS_MNEMONICS);
 
   if (result != views::MenuRunner::MENU_DELETED)
     delete menu_runner;
 }
 
+void VolumeMenuButton::ShowStatusAreaVolume(bool show) {
+  SetVisible(show);
+}
+
 }  // namespace chromeos