Roll PDFium cfb31d6..2f6d148

https://pdfium.googlesource.com/pdfium.git/+log/cfb31d6..2f6d148

BUG=625541,625823

Review-Url: https://codereview.chromium.org/2128163002
Cr-Commit-Position: refs/heads/master@{#404047}