Roll src/third_party/pdfium 5bc1f981df4d..671aece845dd (8 commits)

https://pdfium.googlesource.com/pdfium.git/+log/5bc1f981df4d..671aece845dd

git log 5bc1f981df4d..671aece845dd --date=short --first-parent --format='%ad %ae %s'
2020-04-14 thestig@chromium.org Add FPDFAnnotEmbedderTest.FocusableAnnotRendering.
2020-04-14 thestig@chromium.org Update .gitignore after moving from YASM to NASM.
2020-04-14 tsepez@chromium.org Retain widgets across SetFocus() calls in CXFA_FFWidgetHandler.
2020-04-14 no-reply@google.com Mark static const class/struct members as constexpr
2020-04-14 tsepez@chromium.org Add missing brace to bug_1069700.in
2020-04-14 thestig@chromium.org Sanitize mouse wheel code.
2020-04-14 thestig@chromium.org Add FORM_OnMouseWheel().
2020-04-14 dhoss@chromium.org Add FPDF_GetFileIdentifier() to public API

Created with:
  gclient setdep -r src/third_party/pdfium@671aece845dd

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:1069700,chromium:1069789
Tbr: pdfium-deps-rolls@chromium.org
Change-Id: Ic36a9ccb58506e566bce820ea6a7b20595f610ad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2149524Reviewed-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@{#758994}

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': '5bc1f981df4d02a2c2329891268667a0ff3a4e0f',
+  'pdfium_revision': '671aece845dd17d61a9f223ac41c6a50aa5145c2',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling BoringSSL
   # and whatever else without interference from each other.