Roll PDFium a398ca6..3acb1ef

https://pdfium.googlesource.com/pdfium.git/+log/a398ca6..3acb1ef

BUG=497357,541323,514891
TBR=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1403563002

Cr-Commit-Position: refs/heads/master@{#353405}