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

chrome/browser/chromeos/status/volume_menu_button.cc

Index: chrome/browser/chromeos/status/volume_menu_button.cc
===================================================================
--- chrome/browser/chromeos/status/volume_menu_button.cc	(revision 118753)
+++ chrome/browser/chromeos/status/volume_menu_button.cc	(working copy)
@@ -9,6 +9,7 @@
 #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"
@@ -172,12 +173,16 @@
     : 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() {
@@ -233,4 +238,8 @@
     delete menu_runner;
 }
 
+void VolumeMenuButton::ShowStatusAreaVolume(bool show) {
+  SetVisible(show);
+}
+
 }  // namespace chromeos