Roll PDFium 32b639d..4a2aa1a

https://pdfium.googlesource.com/pdfium.git/+log/32b639d..4a2aa1a

TBR=thakis@chromium.org
BUG=571480

Review URL: https://codereview.chromium.org/1602333002

Cr-Commit-Position: refs/heads/master@{#370257}