Roll src/third_party/pdfium/ c7739322e..37b12ad87 (2 commits).

https://pdfium.googlesource.com/pdfium.git/+log/c7739322e5cd..37b12ad87319

$ git log c7739322e..37b12ad87 --date=short --no-merges --format='%ad %ae %s'
2016-12-14 tsepez Return unique_ptr from CXFA_FFApp::CreateDoc.
2016-12-14 tsepez More unique_ptr returns from DIB methods.

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/2576983002
Cr-Commit-Position: refs/heads/master@{#438753}

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': 'c7739322e5cdcc5779bdde2a1560ea3dee891e51',
+  'pdfium_revision': '37b12ad873198a9644f3de0d2eff001285e1ad42',
   # 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.