Reland "Fix jank on first show of holding space welcome banner."

This is a reland of f5df79ec

Original change's description:
> Fix jank on first show of holding space welcome banner.
>
> Because holding space welcome banner styles are dynamically loaded,
> there was some jank when the banner was shown before the dynamic styles
> had finished loading.
>
> This CL adds inline styles to hide the welcome banner until they are
> removed following load completion of dynamic styles.
>
> Bug: 1170470
> Change-Id: I32aa65c5c17505d1e2c2bee61a4e27468c6f881d
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2649110


> Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
> Commit-Queue: David Black <dmblack@google.com>
> Cr-Commit-Position: refs/heads/master@{#847408}

Bug: 1170470
Change-Id: I03c79e69820730315064fe50d27cfc217ce1adb1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2678984


Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: David Black <dmblack@google.com>
Cr-Commit-Position: refs/heads/master@{#851384}