Roll src/third_party/pdfium 7bb6613a0b68..6489c0e7dc80 (4 commits)

https://pdfium.googlesource.com/pdfium.git/+log/7bb6613a0b68..6489c0e7dc80

git log 7bb6613a0b68..6489c0e7dc80 --date=short --first-parent --format='%ad %ae %s'
2020-03-27 thestig@chromium.org Uninline CFX_WideTextBuf methods.
2020-03-27 thestig@chromium.org Add a missing {{streamlen}} in rectangles.in.
2020-03-26 thestig@chromium.org Fix typo in enum CPDF_Function::Type.
2020-03-26 tsepez@chromium.org Add unit tests for cpdf_function.

Created with:
  gclient setdep -r src/third_party/pdfium@6489c0e7dc80

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: I7683f504d7dd3de1aceab84ea6b956a0414918f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2123984Reviewed-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@{#753941}

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': '7bb6613a0b68569f94e9ff271a111dfe8de88097',
+  'pdfium_revision': '6489c0e7dc806db4363cfc5d91033b4bc83d35bc',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling BoringSSL
   # and whatever else without interference from each other.