Roll src/third_party/pdfium/ 7e7ef3dd6..87dffc031 (1 commit).

https://pdfium.googlesource.com/pdfium.git/+log/7e7ef3dd60a8..87dffc031547

$ git log 7e7ef3dd6..87dffc031 --date=short --no-merges --format='%ad %ae %s'
2016-08-31 dsinclair Free the GifPlainText object when complete.

BUG=638499

TBR=dsinclair@chromium.org

Review-Url: https://codereview.chromium.org/2296183002
Cr-Commit-Position: refs/heads/master@{#415637}

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': '7e7ef3dd60a836521607d4b2ec41cbbe950183f9',
+  'pdfium_revision': '87dffc0315477150c9c1964913b65bc97bdf654f',
   # 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.