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This properly identify redirect chains. Before this CL, each link in the
redirect chain would seem to be initiated by the eventual request,
instead of the previous redirect.

Also logs the number of cases where the redirected request doesn't have
the same initiator as the initial request.

Review URL: https://codereview.chromium.org/1633813005

Cr-Commit-Position: refs/heads/master@{#371522}