Avoid shadowing UNKNOWN (defined in both quic and ftp)

If you include both net/ftp/ftp_directory_listing_parser.h and
net/quic/quic_chromium_client_session.h you get an error
about an UNKNOWN shadowing another UNKNOWN. I don't think this
is a new problem but something we got with a new clang version.

This renames the net::UNKNOWN to net::UNKNOWN_CAUSE so that
net::FtpDirectoryListingEntry::UNKNOWN and other unknown
UNKNOWNs can stay.

net/ftp/ftp_directory_listing_parser.h:21:5: error: declaration shadows a variable in namespace 'net' [-Werror,-Wshadow]
    UNKNOWN,
    ^
net/quic/quic_chromium_client_session.h:83:3: note: previous declaration is here
  UNKNOWN,
  ^
1 error generated.

TBR=zhongyi@chromium.org

Change-Id: I96c6c8ba3b923a691537debbfe468874c767b939
Reviewed-on: https://chromium-review.googlesource.com/c/1326494
Reviewed-by: Daniel Bratell <bratell@opera.com>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#606509}
2 files changed