Roll src/third_party/pdfium/ 4e4d1a662..1d023881c (2 commits).

https://pdfium.googlesource.com/pdfium.git/+log/4e4d1a662b09..1d023881cd53

$ git log 4e4d1a662..1d023881c --date=short --no-merges --format='%ad %ae %s'
2016-10-13 tsepez Make CPDF_Object containers hold objects via unique pointers.
2016-10-13 thestig Optimize roll operator in CPDF_PSEngine some more.

TBR=dsinclair@chromium.org

Review-Url: https://codereview.chromium.org/2415273002
Cr-Commit-Position: refs/heads/master@{#425225}

DEPS

@@ -63,7 +63,7 @@ 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': '4e4d1a662b09d9ee1dc93dd8ee37694d3c4eb519',
+  'pdfium_revision': '1d023881cd53485303c0fcc0b5878e700dc470fd',
   # 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.