Roll PDFium from 634973155ab5 to de8ee4c6b051 (10 revisions)

https://pdfium.googlesource.com/pdfium.git/+log/634973155ab5..de8ee4c6b051

2020-06-02 thestig@chromium.org Make more CFDE_TextOut::Piece pointers const.
2020-06-02 thestig@chromium.org Use size_t in CFDE_TextOut::Line.
2020-06-02 thestig@chromium.org Remove some unnecessary enum keywords.
2020-06-02 thestig@chromium.org Fix enum value style in CFX_Value.
2020-06-02 thestig@chromium.org Give CFDE_TextOut::Line methods/members better names.
2020-06-02 thestig@chromium.org Give CFDE_TextOut inner classes shorter names.
2020-06-02 thestig@chromium.org Flip a conditional in CPDF_RenderStatus::ProcessType3Text().
2020-06-02 thestig@chromium.org Use |m_bPrint| more often in CPDF_RenderStatus.
2020-06-02 nigi@chromium.org Avoid setting FXTEXT_CLEARTYPE when FXTEXT_NOSMOOTH is in use.
2020-06-02 dsinclair@chromium.org Add CONTRIBUTING.md

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: I4d8fbe8407daa0d41ddd92c8fcce5bec695aa789
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2227680Reviewed-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@{#774509}

DEPS

@@ -202,7 +202,7 @@ 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': '634973155ab5f27f443c38292efca94647bff5f9',
+  'pdfium_revision': 'de8ee4c6b0516d51ec262b6935a1afda0763430e',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling BoringSSL
   # and whatever else without interference from each other.