Roll src/third_party/pdfium/ b5902c780..4bbbca488 (7 commits)

https://pdfium.googlesource.com/pdfium.git/+log/b5902c780751..4bbbca4880fd

$ git log b5902c780..4bbbca488 --date=short --no-merges --format='%ad %ae %s'
2018-05-01 thestig Clean up CFX_BidiString.
2018-05-01 hnakashima Fix last character missing from strings in XFA Month Calendar.
2018-05-01 tsepez Check for NULL XFA context even when XFA
2018-05-01 tsepez Make FPDF_Document always be CPDF_Document.
2018-05-01 tsepez Introduce the concept of CPDF_Page::Extension
2018-05-01 dsinclair Fixes XML Instruction handling in CXFA_DocumentParser.
2018-05-01 dsinclair Fix CFX_XML and add unit tests

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: I27d91765e2757686530a97bc8a5142b11b180f89
Reviewed-on: https://chromium-review.googlesource.com/1037912Reviewed-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@{#555175}

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': 'b5902c78075141d9d569a463486d20ccabd78a2d',
+  'pdfium_revision': '4bbbca4880fdff6b106bd935e6cd62f82025ec55',
   # 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.