Create a FakeTetherService, which stubs out TetherService for development.

chrome/browser/chromeos/tether/tether_service_factory.cc

Index: chrome/browser/chromeos/tether/tether_service_factory.cc
diff --git a/chrome/browser/chromeos/tether/tether_service_factory.cc b/chrome/browser/chromeos/tether/tether_service_factory.cc
index da33cc9260605bc7eb70ff385cc0e8cb5adab31c..eef06b3b6c1e080e3ded977a482b950a15addbe5 100644
--- a/chrome/browser/chromeos/tether/tether_service_factory.cc
+++ b/chrome/browser/chromeos/tether/tether_service_factory.cc
@@ -4,10 +4,14 @@
 
 #include "chrome/browser/chromeos/tether/tether_service_factory.h"
 
+#include "base/command_line.h"
 #include "base/memory/singleton.h"
+#include "base/strings/string_number_conversions.h"
+#include "chrome/browser/chromeos/tether/fake_tether_service.h"
 #include "chrome/browser/cryptauth/chrome_cryptauth_service_factory.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/pref_names.h"
+#include "chromeos/chromeos_switches.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "chromeos/network/network_handler.h"
 #include "chromeos/network/network_state_handler.h"
@@ -40,13 +44,29 @@ KeyedService* TetherServiceFactory::BuildServiceInstanceFor(
     content::BrowserContext* context) const {
   DCHECK(chromeos::NetworkHandler::IsInitialized());
 
-  return new TetherService(
-      Profile::FromBrowserContext(context),
-      chromeos::DBusThreadManager::Get()->GetPowerManagerClient(),
-      chromeos::DBusThreadManager::Get()->GetSessionManagerClient(),
-      ChromeCryptAuthServiceFactory::GetForBrowserContext(
-          Profile::FromBrowserContext(context)),
-      chromeos::NetworkHandler::Get()->network_state_handler());
+  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
+  if (command_line->HasSwitch(chromeos::switches::kTetherStub)) {
+    int num_tether_networks = 0;
+    base::StringToInt(
+        command_line->GetSwitchValueASCII(chromeos::switches::kTetherStub),
+        &num_tether_networks);
+
+    return new FakeTetherService(
+        num_tether_networks, Profile::FromBrowserContext(context),
+        chromeos::DBusThreadManager::Get()->GetPowerManagerClient(),
+        chromeos::DBusThreadManager::Get()->GetSessionManagerClient(),
+        ChromeCryptAuthServiceFactory::GetForBrowserContext(
+            Profile::FromBrowserContext(context)),
+        chromeos::NetworkHandler::Get()->network_state_handler());
+  } else {

[stevenjb, 2017/05/23 22:24:33]

no else

[Ryan Hansberry, 2017/05/23 22:53:12]

Done.

+    return new TetherService(
+        Profile::FromBrowserContext(context),
+        chromeos::DBusThreadManager::Get()->GetPowerManagerClient(),
+        chromeos::DBusThreadManager::Get()->GetSessionManagerClient(),
+        ChromeCryptAuthServiceFactory::GetForBrowserContext(
+            Profile::FromBrowserContext(context)),
+        chromeos::NetworkHandler::Get()->network_state_handler());
+  }
 }
 
 void TetherServiceFactory::RegisterProfilePrefs(