Sort unlaunched apps on app list start page by apps grid order.
When recommending, apps now use a small number multiplied by the index of an
item in the apps grid as an app's score if the app has never been launched.
This causes the apps grid order to be used for apps that have never been
launched. The modification is small enough that no apps that have been
launched in the past year should rank lower than an unlaunched app.
BUG=455338
Review URL: https://codereview.chromium.org/
925883003
Cr-Commit-Position: refs/heads/master@{#317218}