Roll src/third_party/pdfium a8817db1767d..6af2de8b2aa5 (6 commits)

https://pdfium.googlesource.com/pdfium.git/+log/a8817db1767d..6af2de8b2aa5

git log a8817db1767d..6af2de8b2aa5 --date=short --first-parent --format='%ad %ae %s'
2020-04-16 thestig@chromium.org Use FT_LOAD_PEDANTIC in CFX_GlyphCache::RenderGlyph().
2020-04-16 dhoss@chromium.org Change implementation of CPDF_FormField::IsItemSelected()
2020-04-16 dhoss@chromium.org Add unit tests for CPDF_FormField::IsItemSelected()
2020-04-16 bravi@microsoft.com Added URI Action handling public API and its test cases
2020-04-16 nigi@chromium.org Fix embedder test FPDFFormFillEmbedderTest.BUG_1281 for Skia.
2020-04-16 dhoss@chromium.org Capture existing multi-select list box behavior with more tests

Created with:
  gclient setdep -r src/third_party/pdfium@6af2de8b2aa5

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:1063609,chromium:994500
Tbr: pdfium-deps-rolls@chromium.org
Change-Id: I468d30ad3ca5077a15c9835f3bc5ba22487264e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2153876Reviewed-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@{#759871}

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': 'a8817db1767dbe6f79782ff00335d819afe296e9',
+  'pdfium_revision': '6af2de8b2aa5819d76ec8f3d533b09c7b39fab49',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling BoringSSL
   # and whatever else without interference from each other.