Roll src/third_party/pdfium/ 3900ddb64..8cfcb7da3 (2 commits)

https://pdfium.googlesource.com/pdfium.git/+log/3900ddb64f30..8cfcb7da3735

$ git log 3900ddb64..8cfcb7da3 --date=short --no-merges --format='%ad %ae %s'
2018-04-17 thestig Fix nits in CPDF_Function and derived classes.
2018-04-17 thestig Implement FORM_GetFocusedText() API.

Created with:
  roll-dep src/third_party/pdfium
BUG=chromium:753216


The AutoRoll server is located here: https://pdfium-roll.skia.org

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.


TBR=dsinclair@chromium.org

Change-Id: Ia31b03d7e641f3fd8613f5f95370d380cdb8d532
Reviewed-on: https://chromium-review.googlesource.com/1015083
Commit-Queue: pdfium-chromium-autoroll <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Reviewed-by: pdfium-chromium-autoroll <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#551393}

DEPS

@@ -110,7 +110,7 @@ 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': '3900ddb64f30f36fd6696bd2927cf8f151e6ede9',
+  'pdfium_revision': '8cfcb7da37352b22517892e6eabcedb77676cdf7',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling openmax_dl
   # and whatever else without interference from each other.