GitLab

Reorganize:
- Move NupPdfToPdf() into the anonymous namespace.
- Make NupPdfToPdf() return a PDF instead of the PDF data.
- Return earlier in PrintPagesAsRasterPDF().

- Make CreateSinglePageRasterPdf() return a ScopedFPDFDocument.
- Put |scale_factor| in the smallest possible scope.
- Group static methods together in the header.
- Use "Pdf" consistently in method names.
- Mark some methods const.

Nits: 
Change-Id: I25ac995d2041990eab42391915a6736044ad6b63
Reviewed-on: https://chromium-review.googlesource.com/1238075
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593432}