[NTP] Change shortcut visibility on toggle

Toggle visibility of the shortcuts on "toggleShortcutsVisibility".

Screencast: https://drive.google.com/open?id=114CXbtG4bDxaUh4jmgjKp8OMS0mV7AR4

Bug: 953822
Change-Id: I0569e4e598af689b67306f71e45065210a0db85f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1653087
Commit-Queue: Kristi Park <kristipark@chromium.org>
Reviewed-by: Kyle Milka <kmilka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#668583}
4 files changed