Roll src/third_party/pdfium/ 53279b1dc..f51cdbd2b (5 commits)

https://pdfium.googlesource.com/pdfium.git/+log/53279b1dcaba..f51cdbd2bddd

$ git log 53279b1dc..f51cdbd2b --date=short --no-merges --format='%ad %ae %s'
2018-02-16 hnakashima Reland "Actually enable -Wimplicit-fallthrough for pdfium."
2018-02-16 rharrison Correct mapping text to characters for characters missing from font
2018-02-16 hnakashima Fix more fallthroughs before reenabling -Wimplicit-fallthrough.
2018-02-16 hnakashima Fix mouse pointer in XFA forms.
2018-02-16 thestig Roll DEPS for clang to a695c30c.

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: I31876b61beaf64714b0894852ed6a0631312ec66
Reviewed-on: https://chromium-review.googlesource.com/924612Reviewed-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@{#537500}

DEPS

@@ -103,7 +103,7 @@ 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': '53279b1dcabae4913f7f0a58e741942e82ab7d59',
+  'pdfium_revision': 'f51cdbd2bddde1de314b69280c97e57ab07dfdc8',
   # 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.