Roll src/third_party/pdfium/ 957480c17..f0f2a2a52 (4 commits)

https://pdfium.googlesource.com/pdfium.git/+log/957480c17682..f0f2a2a528e1

$ git log 957480c17..f0f2a2a52 --date=short --no-merges --format='%ad %ae %s'
2017-06-13 thestig Fix a buffer overflow in FPDFPage_Flatten().
2017-06-13 thestig Fix some nits in CFFL_InteractiveFormFiller.
2017-06-13 thestig Remove deprecated FPDPage_HasFormFieldAtPoint().
2017-06-13 thestig Fix bad format string in CXFA_FM2JSContext.

Created with:
  roll-dep src/third_party/pdfium
BUG=732661,732533


Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, see:
http://www.chromium.org/developers/tree-sheriffs/sheriff-details-chromium#TOC-Failures-due-to-DEPS-rolls


TBR=dsinclair@chromium.org

Change-Id: I7e46b976b0bf8b8de2df9e9f77d5ba2957698833
Reviewed-on: https://chromium-review.googlesource.com/534941
Reviewed-by: <pdfium-deps-roller@chromium.org>
Commit-Queue: <pdfium-deps-roller@chromium.org>
Cr-Commit-Position: refs/heads/master@{#479430}