Roll PDFium from a61a55a444b3 to 8516651130b5 (8 revisions)

https://pdfium.googlesource.com/pdfium.git/+log/a61a55a444b3..8516651130b5

2020-07-14 thestig@chromium.org Add FPDFEditEmbedderTest.ExtractImageBitmapIgnoresSetMatrix.
2020-07-14 nigi@chromium.org Remove unused integer fill flags and converter functions.
2020-07-14 nigi@chromium.org Change FX_FillMode type parameters in CXFA_Graphics.
2020-07-14 tsepez@chromium.org Make CFXJSE_Context delete its own CXFA_ThisProxies.
2020-07-14 thestig@chromium.org Use ScopedFPDFBitmap in FPDFEditEmbedderTest().
2020-07-14 nigi@chromium.org Replace more integer fill types with CFX_FillRenderOptions::FillType.
2020-07-14 nigi@chromium.org Remove usage of FXFILL_WINDING and FXFILL_ALTERNATE in CPDF_ClipPath.
2020-07-14 tsepez@chromium.org Put CJX_Objects into V8 object embedder slots

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: None
Tbr: pdfium-deps-rolls@chromium.org
Change-Id: I1269c3a627baa9ab4557c3005b8fcf38679f8d02
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2299484Reviewed-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@{#788555}

DEPS

@@ -214,7 +214,7 @@ 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': 'a61a55a444b3bff3047de4bcc495d1cf92c76d93',
+  'pdfium_revision': '8516651130b5e2b1a382ad9d9e43e4eccc3abc81',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling BoringSSL
   # and whatever else without interference from each other.