[NTP] Add more variations for the fakebox

Add two more features, FakeboxSearchIconColorOnNtp and
UseAlternateFakeboxRectOnNtp. These will be used to add colored search
icon and rectangular search box variants for the fakebox experiment.

Screenshots: https://drive.google.com/open?id=1sucXl7Z-28vKtx-O5Kp0AVV_3w_Us6UV

Bug: 956164
Change-Id: Ibfc01a08ce5155d85e8ca0830b1e8a4c97764b38
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1585085
Reviewed-by: Ramya Nagarajan <ramyan@chromium.org>
Commit-Queue: Kristi Park <kristipark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654295}
5 files changed