Roll src/third_party/pdfium/ cff5618d4..98909bf9f (2 commits).

https://pdfium.googlesource.com/pdfium.git/+log/cff5618d4e84..98909bf9f458

$ git log cff5618d4..98909bf9f --date=short --no-merges --format='%ad %ae %s'
2017-01-26 dsinclair Add CSS parser tests
2017-01-26 dsinclair Cleanup memory in CFDE_CSSStyleSelector

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

If the roll is causing failures, see:
http://www.chromium.org/developers/tree-sheriffs/sheriff-details-chromium#TOC-Failures-due-to-DEPS-rolls

TBR=dsinclair@chromium.org

Review-Url: https://codereview.chromium.org/2661463002
Cr-Commit-Position: refs/heads/master@{#446375}

DEPS

@@ -64,7 +64,7 @@ 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': 'cff5618d4e847b9f13e1f051d56e09ee00cfb089',
+  'pdfium_revision': '98909bf9f458614abc1bb7f4df34a319a1d5ce3f',
   # 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.