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Originally, it was only used when Print Preview is enabled, but the
original user no longer exists, and the only user is the Settings page.
Transitively only build settings::PrintingHandler when printing is
enabled.

BUG=789790

Change-Id: I8e8b9d0df66b1a5ead01abeeaad78982f16e61ec
Reviewed-on: https://chromium-review.googlesource.com/806447Reviewed-by: Dave Schuyler <dschuyler@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521880}