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

apps/pref_names.h

Index: apps/pref_names.h
diff --git a/apps/pref_names.h b/apps/pref_names.h
index db5d7c2d9ff31d9dfbe9b793ed546b8bde611c2e..27eedb47a626b24c354abc993b00208ede96bc9d 100644
--- a/apps/pref_names.h
+++ b/apps/pref_names.h
@@ -10,9 +10,10 @@ namespace prefs {
 
 // Alphabetical list of preference names specific to Apps component.
 // Keep alphabetized and document each one in the source file.
-extern const char kAppLauncherIsEnabled[];
-extern const char kAppLaunchForMetroRestart[];
 extern const char kAppLaunchForMetroRestartProfile[];
+extern const char kAppLaunchForMetroRestart[];
+extern const char kAppLauncherHasBeenEnabled[];
+extern const char kAppLauncherIsEnabled[];
 extern const char kShowAppLauncherPromo[];
 
 }  // namespace prefs