Roll PDFium from 68bba80440f0 to 9606a2fc6ff0 (5 revisions)

https://pdfium.googlesource.com/pdfium.git/+log/68bba80440f0..9606a2fc6ff0

2022-01-05 tsepez@chromium.org Remove string stream from CFXJSE_FormCalcContext::Stuff()
2022-01-05 tsepez@chromium.org Avoid CHECK() in CFXJSE_FormCalcContext::Stuff()
2022-01-04 thestig@chromium.org Fix DCHECK failure triggered by CXFA_Measurement::SetString().
2022-01-04 thestig@chromium.org Make one branch in CFXJSE_FormCalcContext::Str() faster.
2022-01-04 thestig@chromium.org Add more CXFAMeasurement unit tests.

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 file a bug in PDFium: https://bugs.chromium.org/p/pdfium/issues/entry
To file a bug in Chromium: https://bugs.chromium.org/p/chromium/issues/entry

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/main/autoroll/README.md

Bug: chromium:1282801,chromium:1284171
Tbr: pdfium-deps-rolls@chromium.org
Change-Id: Idbe39bea0a060b81de88d58ac0b30bfdca867473
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3367134
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Bot-Commit: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#955564}