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To help diagnose the broken referrer chain problem to extension inline
install, we want to use Proto instead of JSON as the content format,
such that we can easily add more info to the request.

In addition, when referrer chain appears broken (completely empty, or
missing some entries), we are going to append recent navigation events
(quantity controlled by Finch) and send them for SBER/SCOUT users when
they are not in incognito.

Bug: 780532
Change-Id: I37ee0e6bf7a5e295640fca3eee86cb249595c7f5
Reviewed-on: https://chromium-review.googlesource.com/850726Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Ben Wells <benwells@chromium.org>
Commit-Queue: Jialiu Lin <jialiul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533146}