Refactor the TrayAudio code so that it can be used by other platforms.

ash/ash_switches.cc

Index: ash/ash_switches.cc
diff --git a/ash/ash_switches.cc b/ash/ash_switches.cc
index 12413446f0e3577989c3666cdf1b1e6df85c615c..735bda0e3de855632c631bfa97e89c9804c18dfe 100644
--- a/ash/ash_switches.cc
+++ b/ash/ash_switches.cc
@@ -256,12 +256,16 @@ bool UseDockedWindows() {
   return !CommandLine::ForCurrentProcess()->HasSwitch(kAshDisableDockedWindows);
 }
 
-#if defined(OS_CHROMEOS)
 bool ShowAudioDeviceMenu() {
+#if defined(OS_CHROMEOS)
   return !CommandLine::ForCurrentProcess()->
       HasSwitch(kAshDisableAudioDeviceMenu);
+#else
+  return false;
+#endif
 }
 
+#if defined(OS_CHROMEOS)
 bool UseUsbChargerNotification() {
   return !CommandLine::ForCurrentProcess()->
       HasSwitch(kAshDisableUsbChargerNotification);