Roll PDFium 135b998..b6befb2

https://pdfium.googlesource.com/pdfium.git/+log/135b998..b6befb2

BUG=635008,634716,632622
TBR=thestig@chromium.org

Review-Url: https://codereview.chromium.org/2226163003
Cr-Commit-Position: refs/heads/master@{#410544}