Add a flag to app_shell that allows roaming on cellular networks

extensions/shell/common/switches.h

Index: extensions/shell/common/switches.h
diff --git a/extensions/shell/common/switches.h b/extensions/shell/common/switches.h
index 7fe3d59a7bbaf9717a401e29840361636b6dadf6..b6b393292fe21362d3e2846c1dc2a7bf64f5d95d 100644
--- a/extensions/shell/common/switches.h
+++ b/extensions/shell/common/switches.h
@@ -10,6 +10,7 @@ namespace switches {
 
 // All switches in alphabetical order. The switches should be documented
 // alongside the definition of their values in the .cc file.
+extern const char kAppShellAllowRoaming[];
 extern const char kAppShellHostWindowSize[];
 extern const char kAppShellInstallCrx[];
 extern const char kAppShellPreferredNetwork[];