Pull pdfium to get GN build update.

DEPS

 # This file is automatically processed to create .DEPS.git which is the file
 # that gclient uses under git.
 #
 # See http://code.google.com/p/chromium/wiki/UsingGit
 #
 # To test manually, run:
 #   python tools/deps2git/deps2git.py -o .DEPS.git -w <gclientdir>
 # where <gcliendir> is the absolute path to the directory containing the
 # .gclient file (the parent of 'src').
 #
@@ skipping 44 matching lines @@
   # the commit queue can handle CLs rolling ANGLE
   # and whatever else without interference from each other.
   "angle_revision": "ab56c6aeff8ea52a8927a947ec20d19eb4564fc9",
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling build tools
   # and whatever else without interference from each other.
   'buildtools_revision': 'ea4dc0e322f4c4c3784ace03b47de99184c4cb55',
   # 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': '5f8a503b2a8701c5c4f6e0aadf334affcdd03d28',
+  'pdfium_revision': 'e6e40abd9753c50917c1fc47f10c105ebe489e58',
   # 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.
   'openmax_dl_revision': '79e64bc9243e5ff11822434cf39b9fabefff3bfb',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling BoringSSL
   # and whatever else without interference from each other.
   'boringssl_revision': '6c7aed048ca0a335e02dfee10976c5dc8620783e',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling nss
@@ skipping 719 matching lines @@
     # corresponding .py files have already been deleted.
     'name': 'remove_stale_pyc_files',
     'pattern': 'src/tools/.*\\.py',
     'action': [
         'python',
         'src/tools/remove_stale_pyc_files.py',
         'src/tools',
     ],
   },
 ]