Roll src/third_party/pdfium/ 12ec6760a..c45271e05 (3 commits)

https://pdfium.googlesource.com/pdfium.git/+log/12ec6760afd9..c45271e053c8

$ git log 12ec6760a..c45271e05 --date=short --no-merges --format='%ad %ae %s'
2017-12-05 thestig Remove redundant field in struct FXCMAP_CMap.
2017-12-05 thestig Fix CXFA_SimpleParser member destruction order.
2017-12-05 thestig Avoid integer overflows in CPDF_FixedMatrix::Transform().

Created with:
  roll-dep src/third_party/pdfium
BUG=791616,791048


The AutoRoll server is located here: https://pdfium-roll.skia.org

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

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.


TBR=dsinclair@chromium.org

Change-Id: Id9a3a2c72218d95099dc5a350d51e2050758e565
Reviewed-on: https://chromium-review.googlesource.com/809312
Reviewed-by: <pdfium-deps-roller@chromium.org>
Commit-Queue: <pdfium-deps-roller@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521848}