[NTP] Adds a pill under MD icons text for themes.

Addresses the visibility of NTP icon text by adding a white pill underneath the text. Also, because we no longer need the textshadow, we use the css function to implement the ellipsis instead of writing our own function.

Before:
https://screenshot.googleplex.com/8N6m2yLinvo.png
https://screenshot.googleplex.com/3uCW3TsFzyN.png
After:
https://screenshot.googleplex.com/SbwT1GmCR5W.png
https://screenshot.googleplex.com/xrMjBTji41t.png

The setting doesn't affect the older version mv-tiles:
https://screenshot.googleplex.com/DWtC5dUPqW5.png

Bug: 850718
Change-Id: I002bc972edf2a69d4092b37193ee2fe932ab66f2
Reviewed-on: https://chromium-review.googlesource.com/1148891
Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Commit-Queue: Weilun Shi <sweilun@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578549}
3 files changed