[NTP] Add ability to add/delete/reset custom links from the New Tab Page

Added functionality for adding/removing links and restoring the Most
Visited tiles. If the URL is not valid, the link will not be added. The
blacklist button now opens the edit dialog (editing links is currently
not functional and will be added in a later CL).

Also added hover/pressed/focus styling to the input fields and the
buttons.

Design Doc: go/chrome-ntp-custom-links

Video: https://screencast.googleplex.com/cast/NTQyNDU2OTc1ODI1MzA1NnwwMjFkODAwYi1kMg

Bug: 851293
Change-Id: Ic92e46ba93a4abcb375467a1d047cbb573f231ba
Reviewed-on: https://chromium-review.googlesource.com/1149458
Commit-Queue: Kristi Park <kristipark@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578404}
19 files changed