Remove --show-app-list-shortcut flag and implement new app launcher enable logic.

apps/prefs.cc

Index: apps/prefs.cc
diff --git a/apps/prefs.cc b/apps/prefs.cc
index 2685860d703d61dd79c6762ecc94ec1433fec824..bb7db1d157742d49fa94c25375f6bbaac39f704e 100644
--- a/apps/prefs.cc
+++ b/apps/prefs.cc
@@ -23,6 +23,9 @@ void RegisterPrefs(PrefRegistrySimple* registry) {
 #if defined(OS_WIN)
   registry->RegisterStringPref(prefs::kAppLaunchForMetroRestart, "");
   registry->RegisterStringPref(prefs::kAppLaunchForMetroRestartProfile, "");
+  registry->RegisterBooleanPref(prefs::kAppLauncherHasBeenEnabled, false);
+  registry->RegisterBooleanPref(prefs::kAppLauncherStartMenuShortcutCreated,
+                                false);
 #endif
 
   // Identifies whether we should show the app launcher promo or not.