Roll src/third_party/pdfium e6e9fec904b8..5bc1f981df4d (7 commits)

https://pdfium.googlesource.com/pdfium.git/+log/e6e9fec904b8..5bc1f981df4d

git log e6e9fec904b8..5bc1f981df4d --date=short --first-parent --format='%ad %ae %s'
2020-04-14 dhoss@chromium.org Add a helper to copy a ByteString to a buffer
2020-04-13 thestig@chromium.org Remove third_party/yasm from DEPS.
2020-04-13 thestig@chromium.org Roll third_party/libjpeg_turbo/ ce0e57e8e..7e3ad7980 (4 commits)
2020-04-13 thestig@chromium.org Add third_party/nasm to DEPS.
2020-04-13 thestig@chromium.org Fix nits in the DEPS file.
2020-04-13 tsepez@chromium.org Remove some needless locals from cxfa_ffwidgethandler.cpp
2020-04-13 tsepez@chromium.org Observe pagview across JS invocation in cpdfxfa_page.cpp

Created with:
  gclient setdep -r src/third_party/pdfium@5bc1f981df4d

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:766721
Tbr: pdfium-deps-rolls@chromium.org
Change-Id: I2ec868838e528a83adbec69b7b1f1e00448e91eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2148166Reviewed-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@{#758703}

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': 'e6e9fec904b871b94d1b58690e0917dc3153b7e8',
+  'pdfium_revision': '5bc1f981df4d02a2c2329891268667a0ff3a4e0f',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling BoringSSL
   # and whatever else without interference from each other.