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It's always set to the same value, and it's never actually read (apart
from some DCHECKs).
This also uncovered lots of IWYU violations which this CL fixes.

Bug: none
Change-Id: Idf98478d8fcf81f65ab42b7b9561de0ceff701dc
Reviewed-on: https://chromium-review.googlesource.com/c/1276505
Commit-Queue: Marc Treib <treib@chromium.org>
Reviewed-by: Mohamed Amir Yosef <mamir@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599242}