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

apps/app_launcher.h

Index: apps/app_launcher.h
diff --git a/apps/app_launcher.h b/apps/app_launcher.h
index d3156a1cacbba6e1f46fedbd7252c9b4a56e671c..dbbd87dd7e7583247beaa4ad95ee7d0ab125f6f5 100644
--- a/apps/app_launcher.h
+++ b/apps/app_launcher.h
@@ -13,6 +13,10 @@ namespace apps {
 // 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.
+
 // 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