[ios] Image and styling tweaks to NTP.

 - Update most visited and search icon image.
 - Change hint text to go from 17pt to +.15 scale
 - Center hint text.
 - Make fake omnibox pill-like.
 - Tweak omnibox fade on RxR.

Bug: 857433, 854093, 860414
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ie236f03daf20b074cb4b4382b3c70e79fc9eca9f
Reviewed-on: https://chromium-review.googlesource.com/1138347
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Stepan Khapugin <stkhapugin@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575731}
17 files changed