Roll src/third_party/pdfium/ fff400a5d..6745f96fa (1 commit).

https://pdfium.googlesource.com/pdfium.git/+log/fff400a5df03..6745f96fab41

$ git log fff400a5d..6745f96fa --date=short --no-merges --format='%ad %ae %s'
2017-01-04 tsepez Remove CFX_ArrayTemplate, use unique_ptr in fpdfsdk/pdfwindow

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/2612833002
Cr-Commit-Position: refs/heads/master@{#441446}

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': 'fff400a5df032c2203eef9f76a5dbb164672df3d',
+  'pdfium_revision': '6745f96fab41e2b46f57a3717b034a4064c0de02',
   # 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.