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Add navigation header check to referrer tests

Currently, the referrer browsertests check the outgoing request's
headers on subresource requests but just use JS to check the outgoing
referrer on navigation requests. This patch expands the check to
navigation requests, too, in order to cover more of the navigation
logic.

This patch also
- adds a test covering browser-initiated navigations' referrers
- resolves a few linter complaints (reset -> make_unique; default
constructors)

Change-Id: I804ca43632b881878df63cad33ffaf94b5db6741
Bug: 1021277
Cq-Do-Not-Cancel-Tryjobs: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1924871Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: David Van Cleve <davidvc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#717645}