Improve documentation of CertVerifier::Verify() regarding |out_req|.
Improve documentation of CertVerifier::Verify() regarding |out_req|.

Also adds DISALLOW_COPY() to Request.

BUG=475153

Review URL: https://codereview.chromium.org/1131173005

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#330840}

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