Loader optimization: Reuse already build AppList for package removal & installation

[partipan-dot]

Currently the BroadcastReceiver (AppListChangedReceiver) which listens for Intent.ACTION_PACKAGE_ADDED and Intent.ACTION_PACKAGE_REMOVED calls Loader.onContentChanged(). This calls forceLoad() on the AsyncTaskLoader. It'd be better to update the existing list instead of rebuilding the entire list.