Persist PWA plus install icon across page loads within the app scope

This CL ensures we remember if a site is within a previously seen
installable scope and avoid flashing the PWA install icon redundantly.

Navigations between different installable scopes will still refresh
the PWA install icon and animation.

Before: https://bugs.chromium.org/p/chromium/issues/attachment?aid=383598&signed_aid=00fO__OjzcMdMxXswKP9nQ==&inline=1
After: https://bugs.chromium.org/p/chromium/issues/attachment?aid=383599&signed_aid=8T4ag_9niDNF28Q3N_ggYA==&inline=1

Bug: 907351
Change-Id: Ib21542d44fafb7d6777b6782ba1654266d2e582f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1514282
Commit-Queue: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Auto-Submit: Alan Cutter <alancutter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642935}
11 files changed