External package containing pdfium.

"Insert -> Picture -> From File..." uses this library when a PDF file is
selected.

https://pdfium.googlesource.com/pdfium/

How to update the tarball:

version=$(git for-each-ref|grep chromium/|tail -n 1|sed 's|.*/||')
git archive --prefix=pdfium/ --format=tar origin/chromium/${version} > pdfium-${version}.tar
(cd ..; tar --append --file pdfium/pdfium-${version}.tar pdfium/third_party/freetype/src/include/ pdfium/third_party/freetype/src/src/)
bzip2 pdfium-${version}.tar