Introduce FastShowPickler which will be used for app list cold start.

This class will be responsible for serializing a copy of AppListModel to
populate a dummy AppListView that is shown immediately on startup if
--show-app-list is used.

BUG=178260

Review URL: https://chromiumcodereview.appspot.com/23684003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224699 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 224699