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

apps/app_launcher.h

 // 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.
 
 #ifndef APPS_APP_LAUNCHER_H_
 #define APPS_APP_LAUNCHER_H_
 
 #include "base/callback_forward.h"
 
 namespace apps {
 
 // Called on the UI thread after determining if the launcher is enabled. A
 // boolean flag is passed, which is true if the app launcher is enabled.
 typedef base::Callback<void(bool)> OnAppLauncherEnabledCompleted;
 
+// TODO(calamity): Remove all the "uncertain" apis because windows app launcher
+// enabled is now just a single pref that we can check synchronously and with
+// confidence. This includes changing GetIsAppLauncherEnabled to a synchronous
+// API.
+
 // A synchronous check to determine if the app launcher is enabled. If the
 // registry needs to be determined to find an accurate answer, this function
 // will NOT do so; instead if will default to false (the app launcher is not
 // enabled).
 // This function does not use the cached preference of whether the launcher
 // was enabled or not.
 bool MaybeIsAppLauncherEnabled();
 
 // Determine whether the app launcher is enabled or not. This may involve a trip
 // to a blocking thread. |completion_callback| is called when an answer is
 // ready. This needs to be called on the UI thread.
 void GetIsAppLauncherEnabled(
     const OnAppLauncherEnabledCompleted& completion_callback);
 
 // Returns whether the app launcher was enabled the last time it was checked.
 bool WasAppLauncherEnabled();
 
 }  // namespace apps
 
 #endif  // APPS_APP_LAUNCHER_H_