Split printer installation and printer saving on CupsPrintersManager

This change removes the side effect of saving a printer when it is
marked as installed with CUPS. Printer installation is now separate
from printer saving. Callers are now responsible for calling
SavePrinter() if putting the printer in the saved class is desired.

Bug: 951138
Change-Id: Ice258eeb7ad99f0d8942e3822a6a2f4b0f37249e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1577591
Commit-Queue: Bailey Berro <baileyberro@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Sean Kau <skau@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#657822}
12 files changed