Roll src/third_party/pdfium bf5be75f420c..c171a2106b2b (3 commits)

https://pdfium.googlesource.com/pdfium.git/+log/bf5be75f420c..c171a2106b2b

git log bf5be75f420c..c171a2106b2b --date=short --no-merges --format='%ad %ae %s'
2019-09-23 thestig@chromium.org Split shading rendering code into its own file.
2019-09-23 nigi@chromium.org Fix the TrueType font not rendered correctly issue.
2019-09-23 thestig@chromium.org Add a test for a checkbox that does not print.

Created with:
  gclient setdep -r src/third_party/pdfium@c171a2106b2b

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/pdfium-autoroll
Please CC pdfium-deps-rolls@chromium.org on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

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

TBR=pdfium-deps-rolls@chromium.org

Bug: chromium:861842
Change-Id: I3604d12cde621e4abd689d4d48e2c6cdac78adb6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1819133Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#699007}

DEPS

@@ -182,7 +182,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFium
   # and whatever else without interference from each other.
-  'pdfium_revision': 'bf5be75f420ce3882089ba05a01f93ad43284db2',
+  'pdfium_revision': 'c171a2106b2b70c38f7cca7c26da9b67c413d05d',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling BoringSSL
   # and whatever else without interference from each other.