Roll PDFium 640c395..4ea0e6b

      https://pdfium.googlesource.com/pdfium.git/+log/640c395..4ea0e6b

BUG=507316,529310
TBR=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1335493002

Cr-Commit-Position: refs/heads/master@{#348119}