GitLab

Replace UpdatePrintedDocument(nullptr) with ClearPrintedDocument().
The two methods are simpler to understand than the existing combined
method.

Also get rid of all "new" uses in PrintJob.

Change-Id: I55a51233b0cc9f30c45301703e57b311738f3891
Reviewed-on: https://chromium-review.googlesource.com/1000956Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550637}