Roll src/third_party/pdfium/ fc9b11358..21b111fcf (2 commits).

https://pdfium.googlesource.com/pdfium.git/+log/fc9b11358a47..21b111fcf71e

$ git log fc9b11358..21b111fcf --date=short --no-merges --format='%ad %ae %s'
2016-08-31 thestig Attempt to fix potential integer overflow in CFX_FaceCache::LoadGlyphPath().
2016-08-31 dsinclair Use CheckedNumeric for strength calculation.

BUG=641333,639506

TBR=dsinclair@chromium.org

Review-Url: https://codereview.chromium.org/2300793002
Cr-Commit-Position: refs/heads/master@{#415766}

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': 'fc9b11358a47e1dd9b257263c9457d7e53b9dd10',
+  'pdfium_revision': '21b111fcf71e4e189035f29606ca9d3fdf3ebd92',
   # 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.