GitLab

PDFiumPrint and PDFiumEngineExports both have code to create N-up PDFs.
Merge the two since they are nearly identical.

For the PDFiumPrint caller, make it do fit the page into a symmetrical
printable area, so N-up printing is consistent for PDF content and web
content.

BUG=890058

Change-Id: I933b899434f3a3cd2d853529696629aed18461e7
Reviewed-on: https://chromium-review.googlesource.com/1250162
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595303}