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

apps/prefs.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "apps/prefs.h"
 
 #include "apps/app_launcher.h"
 #include "apps/pref_names.h"
 #include "base/prefs/pref_registry_simple.h"
 
 namespace apps {
 
 void RegisterPrefs(PrefRegistrySimple* registry) {
   // This pref is a cache of the value from the registry the last time it was
   // checked.
   //
   // During the pref initialization, if it is impossible to synchronously
   // determine whether the app launcher is enabled, assume it is disabled.
   // Anything that needs to know the absolute truth should call
   // 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