Roll src/third_party/pdfium 83d503bc728e..b7902da1d4b4 (4 commits)

https://pdfium.googlesource.com/pdfium.git/+log/83d503bc728e..b7902da1d4b4

git log 83d503bc728e..b7902da1d4b4 --date=short --first-parent --format='%ad %ae %s'
2020-03-13 tsepez@chromium.org Cleanup CFX_CSSSyntaxParser.
2020-03-13 tsepez@chromium.org Cleanup CFX_CSSTextBuf.
2020-03-13 tsepez@chromium.org Consolidate some V8 type conversion code.
2020-03-12 thestig@chromium.org Remove unnecessary CheckedNumeric usage in CPDF_DataAvail.

Created with:
  gclient setdep -r src/third_party/pdfium@b7902da1d4b4

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: None
Tbr: pdfium-deps-rolls@chromium.org
Change-Id: I2615c6236f3f595fe441d2ef5c01feb6ea1bb077
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2103262Reviewed-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@{#750295}

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': '83d503bc728e8a42d500727f3982de21c02f406b',
+  'pdfium_revision': 'b7902da1d4b4c3c84b0a1e27dc39bacd488b0597',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling BoringSSL
   # and whatever else without interference from each other.