Create a FakeTetherService, which stubs out TetherService for development.

chromeos/chromeos_switches.cc

Index: chromeos/chromeos_switches.cc
diff --git a/chromeos/chromeos_switches.cc b/chromeos/chromeos_switches.cc
index 7b0e398e450a627dfd40be290ebe917719b75677..93e179be25775883786234c80d7ee626d67dd97f 100644
--- a/chromeos/chromeos_switches.cc
+++ b/chromeos/chromeos_switches.cc
@@ -278,6 +278,10 @@ const char kEnableKioskMode[] = "enable-kiosk-mode";
 // Enables tethering to nearby LTE devices.
 const char kEnableTether[] = "enable-tether";
 
+// Overrides Tether with stub service. Provide integer arguments for the number
+// of fake networks desired, e.g. 'tether-stub=2'.
+const char kTetherStub[] = "tether-stub";
+
 // Disables material design OOBE UI.
 const char kDisableMdOobe[] = "disable-md-oobe";