Add a flag to app_shell that allows roaming on cellular networks

extensions/shell/browser/shell_network_controller_chromeos.cc

Index: extensions/shell/browser/shell_network_controller_chromeos.cc
diff --git a/extensions/shell/browser/shell_network_controller_chromeos.cc b/extensions/shell/browser/shell_network_controller_chromeos.cc
index 1a0d5258b16c80d054486f703921e4a14f88dc16..4ff45c70b6227880ebe3421c5030f47937edcfac 100644
--- a/extensions/shell/browser/shell_network_controller_chromeos.cc
+++ b/extensions/shell/browser/shell_network_controller_chromeos.cc
@@ -10,6 +10,7 @@
 #include "base/strings/stringprintf.h"
 #include "base/time/time.h"
 #include "chromeos/network/network_connection_handler.h"
+#include "chromeos/network/network_device_handler.h"
 #include "chromeos/network/network_handler.h"
 #include "chromeos/network/network_handler_callbacks.h"
 #include "chromeos/network/network_state.h"
@@ -102,6 +103,12 @@ void ShellNetworkController::NetworkConnectionStateChanged(
   }
 }
 
+void ShellNetworkController::SetCellularAllowRoaming(bool allow_roaming) {
+  chromeos::NetworkDeviceHandler* device_handler =
+      chromeos::NetworkHandler::Get()->network_device_handler();
+  device_handler->SetCellularAllowRoaming(allow_roaming);
+}
+
 const chromeos::NetworkState* ShellNetworkController::GetActiveWiFiNetwork() {
   chromeos::NetworkStateHandler* state_handler =
       chromeos::NetworkHandler::Get()->network_state_handler();