Add a flag to app_shell that allows roaming on cellular networks

extensions/shell/browser/shell_browser_main_parts.cc

Index: extensions/shell/browser/shell_browser_main_parts.cc
diff --git a/extensions/shell/browser/shell_browser_main_parts.cc b/extensions/shell/browser/shell_browser_main_parts.cc
index 5ee89cb642dde273a1abbe41a13f3386e7d85426..80deb9dafeb1c1d66120b5b1a269479470a8b222 100644
--- a/extensions/shell/browser/shell_browser_main_parts.cc
+++ b/extensions/shell/browser/shell_browser_main_parts.cc
@@ -113,6 +113,12 @@ void ShellBrowserMainParts::PostMainMessageLoopStart() {
   network_controller_.reset(new ShellNetworkController(
       base::CommandLine::ForCurrentProcess()->GetSwitchValueNative(
           switches::kAppShellPreferredNetwork)));
+
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kAppShellAllowRoaming)) {
+    network_controller_->SetCellularAllowRoaming(true);
+  }
+
 #else
   // Non-Chrome OS platforms are for developer convenience, so use a test IME.
   ui::InitializeInputMethodForTesting();