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There's a bunch of custom measure, draw and tint  code that appears to be no
longer needed. I suspect it was left over from our non-Modern design and
from when Android support library didn't have tinting support built in.

Also remove unused btn_new_tab_white* assets.

BUG=897345

Change-Id: Ie3b67573371b58ecbef9f9f47518f704435e4180
Reviewed-on: https://chromium-review.googlesource.com/c/1292553
Commit-Queue: Theresa <twellington@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601634}