Roll src/third_party/pdfium/ a31da74cf..c29fc707b (1 commit).

https://pdfium.googlesource.com/pdfium.git/+log/a31da74cffa8..c29fc707b24b

$ git log a31da74cf..c29fc707b --date=short --no-merges --format='%ad %ae %s'
2016-09-08 weili Fix memory management errors for font loading and copying

TBR=dsinclair@chromium.org

Review-Url: https://codereview.chromium.org/2324933002
Cr-Commit-Position: refs/heads/master@{#417401}

DEPS

@@ -60,7 +60,7 @@ 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': 'a31da74cffa8c3ff919051cc49bc006aeb55d345',
+  'pdfium_revision': 'c29fc707b24b9528e41a242cfa298275708ffc76',
   # 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.