Update to whitelist PDFium

[simonhong]

Issue: brave/brave-browser#3846

[simonhong]

cc @bsclifton I can't edit reviewer/assignees list in this repo.

[bsclifton]

++

[bsclifton]

@pilgrim-brave @bbondy anything needed after the merge?

When I did the PDF.js removal code, it looked like all we needed to do was update DEPS file in brave-core. Can you confirm?

[bbondy]

just noting that this will put it on the whitelist for all channels that use this whitelist / blacklist.
I don't think that will cause any problems but just making sure @pilgrim-brave ?

[pilgrim-brave]

AFAIK users can't install PDFium manually, so this should be fine.

[bsclifton]

@bbondy should only take effect (AFAIK) if DEPS gets updated for other channels, right? When asking above, I couldn't remember if this gets packaged with the CRX packaging... I don't think it is, since it's called out in DEPS (doesn't show in brave://components/ either, so I think we're good)

[bbondy]

I think it's used in the local files brave/brave-core-crx-packager, so that means 1 extension for all channels. It's ok though.