Roll pdfium. This brings in:

6256a14  Fix pdfium building issue on VS2010
5eb9f7b  pdfium: Fix all -Wdelete-non-virtual-dtor violations on Mac.
a9c29e0  Fix garbled text when loading linearized pdf document
c7cd3c8  Fix building pdfium for x64 with ninja under windows.
3fb18f4  Hook up the default v8::Platform implementation to pdfium

BUG=260112, 249006, 275281, 354966, 365302, 236952
TBR=thestig@chromium.org

Review URL: https://codereview.chromium.org/398273003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284172 0039d316-1c4b-4281-b951-d872f2087c98

DEPS

@@ -77,7 +77,7 @@ 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": "3fb18f41076a111e48cd8cdaee596075c89c275c",
+  "pdfium_revision": "6256a14279e46f1e893a32bf5102d698fe111cfa",
   # 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.