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Unless we reconstruct an already sanitized referrer from the referrer
url and the referrer policy, we should always sanitize it before
constructing a request from it.

BUG=454621,422871
R=mkwst@chromium.org,jam@chromium.org

Review URL: https://codereview.chromium.org/898613004

Cr-Commit-Position: refs/heads/master@{#315360}