mash: Add SystemTrayClient interface, use to show date settings

ash/mus/system_tray_delegate_mus.cc

Index: ash/mus/system_tray_delegate_mus.cc
diff --git a/ash/mus/system_tray_delegate_mus.cc b/ash/mus/system_tray_delegate_mus.cc
index 8add535aa2bf63f0e61f51d57121d91a21396604..cb91ccd11b10988daabf14d58d3bf24469861e29 100644
--- a/ash/mus/system_tray_delegate_mus.cc
+++ b/ash/mus/system_tray_delegate_mus.cc
@@ -36,6 +36,18 @@ base::HourClockType SystemTrayDelegateMus::GetHourClockType() const {
   return hour_clock_type_;
 }
 
+void SystemTrayDelegateMus::ShowDateSettings() {
+  system_tray_client_->ShowDateSettings();

[James Cook, 2016/09/22 23:19:18]

Is there a naming convention for these interfaceptr member variables so that the
reader knows this is an IPC and not just a regular function call?

I previously just called it client_, but that seemed too vague.

[sky, 2016/09/23 16:42:26]

How do you know SetClient() has been called by the time you get here?

[sky, 2016/09/23 16:42:26]

'client_' is actually used a fair amount. And no, there isn't a naming
convention that conveys the IPC call.

+}
+
+void SystemTrayDelegateMus::SetClient(
+    mojom::SystemTrayClientPtr system_tray_client) {
+  DCHECK(system_tray_client);
+  DCHECK(!system_tray_client_);
+  system_tray_client_ = std::move(system_tray_client);
+  // No special client connection error handling.

[James Cook, 2016/09/22 23:19:18]

Not sure if I need set_connection_error_handler() here.

[sky, 2016/09/23 16:42:25]

It's only necessary if you want to take action if the client is destroyed. I
think the action you want to take is resetting special_tray_client_. That way if
SetClient is called again you don't DCHECK. Say for example chrome crashes then
comes up again.

+}
+
 void SystemTrayDelegateMus::SetUse24HourClock(bool use_24_hour) {
   hour_clock_type_ = use_24_hour ? base::k24HourClock : base::k12HourClock;
   WmShell::Get()->system_tray_notifier()->NotifyDateFormatChanged();