Normalize rotations read from PDF documents. Make FPDFPage_GetRotation
always return a value 0 to 3 as specified in fpdf_edit.h instead of
returning the page rotation / 90 (page rotation may be negative for some
PDFs).
BUG=chromium:713197
Change-Id: Ie477803f7d298b777a3ace89b21cfda8b7f6808b
Reviewed-on: https://pdfium-review.googlesource.com/4532
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>