Add a new App launcher promo to the apps page / NTP.

apps/prefs.cc

Index: apps/prefs.cc
diff --git a/apps/prefs.cc b/apps/prefs.cc
index b883fbb456c23e89191057cfba300fc9a1834a88..dcb042b7a1b946a3de994e8bf8967707fc11dee9 100644
--- a/apps/prefs.cc
+++ b/apps/prefs.cc
@@ -20,6 +20,11 @@ void RegisterPrefs(PrefRegistrySimple* registry) {
   // GetIsAppLauncherEnabled().
   registry->RegisterBooleanPref(prefs::kAppLauncherIsEnabled,
                                 MaybeIsAppLauncherEnabled());
+
+  // Identifies whether we should show the app launcher promo or not.
+  // Now that a field trial also controls the showing, so the promo won't show
+  // unless the pref is set AND the field trial is set to a proper group.
+  registry->RegisterBooleanPref(prefs::kShowAppLauncherPromo, true);
 }
 
 }  // namespace apps