Roll src/third_party/pdfium f22b4e2f6682..c15c0b3a1e9a (3 commits)

https://pdfium.googlesource.com/pdfium.git/+log/f22b4e2f6682..c15c0b3a1e9a


git log f22b4e2f6682..c15c0b3a1e9a --date=short --no-merges --format='%ad %ae %s'
2018-07-18 thestig@chromium.org Roll third_party/skia/ af7700265..588f87967 (1391 commits; 41 trivial rolls)
2018-07-18 thestig@chromium.org Handle wrong tag element count in littlecms.
2018-07-18 tsepez@chromium.org Add pdfium::span::as_bytes() and as_writable_bytes().


Created with:
  gclient setdep -r src/third_party/pdfium@c15c0b3a1e9a

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.



BUG=chromium:864932
TBR=dsinclair@chromium.org

Change-Id: If7555664cbb89a71e68d034eacbb6b6be0e87415
Reviewed-on: https://chromium-review.googlesource.com/1142172
Reviewed-by: pdfium-chromium-autoroll <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Commit-Queue: pdfium-chromium-autoroll <pdfium-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#576322}