Roll PDFium from 0c55cdde36c8 to 6bd8e303c90e (8 revisions)

https://pdfium.googlesource.com/pdfium.git/+log/0c55cdde36c8..6bd8e303c90e

2020-06-30 tsepez@chromium.org Pass cppgc::Heap into xfa layout layer.
2020-06-29 thestig@chromium.org Initialize CFWL_WidgetMgr::Item in the header.
2020-06-29 thestig@chromium.org Initialize CXFA_Graphics::TInfo in the header.
2020-06-29 thestig@chromium.org Initialize various nullptrs where declared.
2020-06-29 thestig@chromium.org Clean up Gouraud / Mesh shading code.
2020-06-29 thestig@chromium.org Add a pixel test with a free-form Gouraud-shaded triangle mesh.
2020-06-29 thestig@chromium.org Fix regression in CFX_SkiaDeviceDriver::PaintStroke().
2020-06-29 pdfium-autoroll@skia-public.iam.gserviceaccount.com Roll Catapult from 91fa1462a88f to a2a7e05eb765 (74 revisions)

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/+doc/master/autoroll/README.md

Bug: chromium:1099990
Tbr: pdfium-deps-rolls@chromium.org
Change-Id: I1e5200fd31c987155d975d6583a265a14b445246
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2275150Reviewed-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@{#783852}

DEPS

@@ -208,7 +208,7 @@ 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': '0c55cdde36c8c9fe1869e8ac275be0550f24a1ab',
+  'pdfium_revision': '6bd8e303c90e42e026c7442caaa477f725150b7b',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling BoringSSL
   # and whatever else without interference from each other.