Fix title of the VPN detailed view in Ash system menu

Title for the VPN detailed view should be "Private Network". Currently,
it wrongly shows "Network".

BUG=663459

Review-Url: https://codereview.chromium.org/2503783002
Cr-Commit-Position: refs/heads/master@{#432671}

ash/common/system/chromeos/network/network_state_list_detailed_view.cc

@@ -374,7 +374,9 @@ void NetworkStateListDetailedView::Init() {
   CreateScrollableList();
   if (!UseMd())
     CreateNetworkExtra();
-  CreateTitleRow(IDS_ASH_STATUS_TRAY_NETWORK);
+  CreateTitleRow(list_type_ == ListType::LIST_TYPE_NETWORK
+                     ? IDS_ASH_STATUS_TRAY_NETWORK
+                     : IDS_ASH_STATUS_TRAY_VPN);
 
   network_list_view_->set_container(scroll_content());
   Update();