Roll src/third_party/pdfium/ f56d93f8e..7b68f616e (1 commit).

https://pdfium.googlesource.com/pdfium.git/+log/f56d93f8ea1c..7b68f616e492

$ git log f56d93f8e..7b68f616e --date=short --no-merges --format='%ad %ae %s'
2016-09-07 tsepez Make Observers into a templated class

TBR=dsinclair@chromium.org

Review-Url: https://codereview.chromium.org/2321493003
Cr-Commit-Position: refs/heads/master@{#417138}

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': 'f56d93f8ea1c2145401e99e61cefdbfcb7341229',
+  'pdfium_revision': '7b68f616e49235267eeac8db51aadade6d60e243',
   # 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.