chromeos: Refactor system tray ShowNetworkSettingsForGuid for mash

ash/public/interfaces/system_tray.mojom

Index: ash/public/interfaces/system_tray.mojom
diff --git a/ash/public/interfaces/system_tray.mojom b/ash/public/interfaces/system_tray.mojom
index 68caeb65b7c2db5c7fbc767d751a8cb77c3d2ced..3cdb3e1be62fa1c0bef936d903d4ced558ce454d 100644
--- a/ash/public/interfaces/system_tray.mojom
+++ b/ash/public/interfaces/system_tray.mojom
@@ -22,8 +22,6 @@ interface SystemTrayClient {
 
   // TODO(crbug.com/647412): ShowSetTimeDialog();
 
-  // TODO(crbug.com/647412): ShowNetworkSettingsForGuid(string guid);
-
   // Shows settings related to multiple displays.
   ShowDisplaySettings();
 
@@ -56,6 +54,12 @@ interface SystemTrayClient {
 
   // TODO(crbug.com/647412): ShowEnterpriseInfo();
 
+  // Shows settings related to networking. If |network_id| is empty, shows
+  // general settings. Otherwise shows settings for the individual network.
+  // On devices |network_id| is a GUID, but on Linux desktop and in tests it can
+  // be any string.
+  ShowNetworkSettings(string network_id);
+
   // Shows UI for changing proxy settings.
   ShowProxySettings();
 };