Roll src/third_party/pdfium/ 89f8fa869..79db60994 (3 commits).

https://pdfium.googlesource.com/pdfium.git/+log/89f8fa8694bb..79db609948b0

$ git log 89f8fa869..79db60994 --date=short --no-merges --format='%ad %ae %s'
2016-09-14 dsinclair Rename CPDFDoc_Environment to CPDFSDK_Environment
2016-09-14 dsinclair Split CPDFXFA_Document apart
2016-09-14 dsinclair Cleanup CPDFXFA_Document.

TBR=dsinclair@chromium.org

Review-Url: https://codereview.chromium.org/2338273003
Cr-Commit-Position: refs/heads/master@{#418570}

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': '89f8fa8694bbf209412845c250af48bbc539962b',
+  'pdfium_revision': '79db609948b01d7a27824b74acc4bd22c8bfd17b',
   # 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.