Remove more usages of WebDocumentLoader::GetRequest

There will be no request once we stop using WebURLLoader
for navigations.

This patch exposes some bits of WebURLRequest instead of
request itself.

TBR=vakh@chromium.org

Bug: 855189
Change-Id: I909fa33480392610d7205cc345f26ff9aa2091d6
Reviewed-on: https://chromium-review.googlesource.com/c/1385146
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Nate Chapin <japhet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618676}
10 files changed