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The reason to stop using URL{Request,Response} for HTTP server interfaces: some
fields of those structs belong to a higher level, e.g., |auto_follow_redirects|.
It seems cleaner to define Http{Request,Response} which match the HTTP
request/response definitions.

BUG=478249
TEST=None

Review URL: https://codereview.chromium.org/1129143005

Cr-Commit-Position: refs/heads/master@{#330238}