Roll src/third_party/pdfium/ 602f06cfb..18f7fbca4 (5 commits)

https://pdfium.googlesource.com/pdfium.git/+log/602f06cfb107..18f7fbca4612

$ git log 602f06cfb..18f7fbca4 --date=short --no-merges --format='%ad %ae %s'
2018-05-24 thestig Mark some pointers as non-const in CPDF_NameTree.
2018-05-24 thestig Improve constness for more CPDF_Objects pointers.
2018-05-23 thestig Remove GetBits32().
2018-05-23 thestig Avoid repeated calculations in CFX_BitStream::GetBits().
2018-05-23 thestig Add unit test for CFX_BitStream.

Created with:
  roll-dep src/third_party/pdfium


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: Ia95af36aa7ddcdf1ae8e677e1cdc454719f0a97b
Reviewed-on: https://chromium-review.googlesource.com/1071167Reviewed-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@{#561410}

DEPS

@@ -120,7 +120,7 @@ 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': '602f06cfb1079cb0153acba75dd94140c58d7b7b',
+  'pdfium_revision': '18f7fbca461254cc0df1af2ca586df42b7fd6c17',
   # 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.