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This patch add methods to CupsPrinterHandler that allow to query a list
of printers from a print server with given URL. Returned list of printers
is compared with the cuurent list of saved printers. This patch adds also
enum PrintServerQueryResult with error codes for ServerPrintersFetcher.

BUG=chromium:1014760
TEST=on my workstation

Change-Id: I14f5d2a68c5ec0621b3e1190622a2bca291d4603
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1912918
Commit-Queue: Piotr Pawliczek <pawliczek@chromium.org>
Auto-Submit: Piotr Pawliczek <pawliczek@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Luum Habtemariam <luum@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715587}