Create system tray item for accessing chrome://slow

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 f726a8f96eeae894996a73cf436297a608834057..73f619586fdaf0daf16530726789b3f45fb4b5eb 100644
--- a/ash/system/tray/system_tray_notifier.cc
+++ b/ash/system/tray/system_tray_notifier.cc
@@ -106,6 +106,14 @@ void SystemTrayNotifier::RemoveSessionLengthLimitObserver(
   session_length_limit_observers_.RemoveObserver(observer);
 }
 
+void SystemTrayNotifier::AddTracingObserver(TracingObserver* observer) {
+  tracing_observers_.AddObserver(observer);
+}
+
+void SystemTrayNotifier::RemoveTracingObserver(TracingObserver* observer) {
+  tracing_observers_.RemoveObserver(observer);
+}
+
 void SystemTrayNotifier::AddUpdateObserver(UpdateObserver* observer) {
   update_observers_.AddObserver(observer);
 }
@@ -179,6 +187,13 @@ void SystemTrayNotifier::NotifyAccessibilityModeChanged(
       OnAccessibilityModeChanged(notify));
 }
 
+void SystemTrayNotifier::NotifyTracingModeChanged(bool value) {
+  FOR_EACH_OBSERVER(
+      TracingObserver,
+      tracing_observers_,
+      OnTracingModeChanged(value));
+}
+
 void SystemTrayNotifier::NotifyRefreshBluetooth() {
   FOR_EACH_OBSERVER(BluetoothObserver,
                     bluetooth_observers_,