Disable -Wshift-negative-value on the tot bots.
Disable -Wshift-negative-value on the tot bots.

It's a new warning and Chromium doesn't build with it.

BUG=507717
TBR=rnk

Review URL: https://codereview.chromium.org/1221083009.

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#337662}

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