Roll src/third_party/pdfium 6e167903252f..4745a47b272f (6 commits)

https://pdfium.googlesource.com/pdfium.git/+log/6e167903252f..4745a47b272f

git log 6e167903252f..4745a47b272f --date=short --first-parent --format='%ad %ae %s'
2020-02-27 thestig@chromium.org Clean up ReportUnsupportedFeatures().
2020-02-27 thestig@chromium.org Make ReportUnsupportedXFA() more efficient.
2020-02-27 dhoss@chromium.org Space-efficiently destroy chained CXFA_FMSimpleExpression instances
2020-02-27 dhoss@chromium.org Create abstract class CXFA_FMChainableExpression
2020-02-27 thestig@chromium.org Handle case of nothing to restore in SkiaState::ClipRestore().
2020-02-26 thestig@chromium.org Roll DEPS for build/ and tools/clang/

Created with:
  gclient setdep -r src/third_party/pdfium@4745a47b272f

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

Bug: chromium:1052724,chromium:986108
Tbr: pdfium-deps-rolls@chromium.org
Change-Id: I4345a5910c260f0309fbd45efc25e2627469c669
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2079036Reviewed-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@{#745208}

DEPS

@@ -195,7 +195,7 @@ 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': '6e167903252fe525c8481a5cced9c67b3aa4b899',
+  'pdfium_revision': '4745a47b272fe1eeae0c5159cc479c541f744fc5',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling BoringSSL
   # and whatever else without interference from each other.