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This is a partial reland of
https://chromium-review.googlesource.com/c/chromium/src/+/1635827
for the task traits additions that were already LGTM'ed.

TBR=fdoray@chromium.org

Bug: 968047
Change-Id: I2dc33aadae040b12e58157c80c343a055ed441f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1762417
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688689}