Roll src/third_party/pdfium/ 6a5c20cd0..1835a6fb9 (1 commit)

https://pdfium.googlesource.com/pdfium.git/+log/6a5c20cd0874..1835a6fb9828

$ git log 6a5c20cd0..1835a6fb9 --date=short --no-merges --format='%ad %ae %s'
2017-04-07 tsepez Tweak CFDF_Font::AppendChar()

Created with:
  roll-dep src/third_party/pdfium

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/2804363002
Cr-Commit-Position: refs/heads/master@{#463014}

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': '6a5c20cd08748da5969cbab756c3e8a6dd27bfbc',
+  'pdfium_revision': '1835a6fb98286817cdf656f4d1e223bd85ee378f',
   # 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.