mash: Move TrayTracing to //ash/common/system/chromeos

ash/system/tray/system_tray_notifier.cc

Index: ash/system/tray/system_tray_notifier.cc
diff --git a/ash/system/tray/system_tray_notifier.cc b/ash/system/tray/system_tray_notifier.cc
index 1520b8eea71aedca2611f036919be0537d0ff798..5e4153ae1d1b4b0d6799f7abe899de6d2d6ac018 100644
--- a/ash/system/tray/system_tray_notifier.cc
+++ b/ash/system/tray/system_tray_notifier.cc
@@ -12,14 +12,6 @@ SystemTrayNotifier::SystemTrayNotifier() {
 SystemTrayNotifier::~SystemTrayNotifier() {
 }
 
-void SystemTrayNotifier::AddTracingObserver(TracingObserver* observer) {
-  tracing_observers_.AddObserver(observer);
-}
-
-void SystemTrayNotifier::RemoveTracingObserver(TracingObserver* observer) {
-  tracing_observers_.RemoveObserver(observer);
-}
-
 void SystemTrayNotifier::AddUserObserver(UserObserver* observer) {
   user_observers_.AddObserver(observer);
 }
@@ -128,13 +120,6 @@ void SystemTrayNotifier::RemoveLastWindowClosedObserver(
 
 #endif  // defined(OS_CHROMEOS)
 
-void SystemTrayNotifier::NotifyTracingModeChanged(bool value) {
-  FOR_EACH_OBSERVER(
-      TracingObserver,
-      tracing_observers_,
-      OnTracingModeChanged(value));
-}
-
 void SystemTrayNotifier::NotifyUserUpdate() {
   FOR_EACH_OBSERVER(UserObserver,
                     user_observers_,