Reload: "Request desktop site" feature should ask reposting

Now Android Chrome does not confirm if it is expected to repost a form
on selecting "Request desktop site".

This change modifies to ask it as we do in other cases.

If a user reject reposting, the navigation switches to use desktop user
agent strings as usuals, but only for the next navigation and
following ones.

BUG=675522
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2587923002
Cr-Commit-Position: refs/heads/master@{#439727}
1 file changed