Making GrGpuResource::release public for special case in Blink

BUG=440462

Review URL: https://codereview.chromium.org/739383006
Replace EncodeBitmap with an interface.

Gives more flexibility to the caller to decide whether to use the
encoded data returned by refEncodedData().

Provides an implementation that supports the old version of
SkPicture::serialize().

TODO: Update Chrome, so we can remove SK_LEGACY_ENCODE_BITMAP entirely

BUG=skia:3190

Review URL: https://codereview.chromium.org/784643002
Force embedding full font when serializing pictures.

We can't do this unconditionally or pipe will become stupidly slow.

DM's serialize mode fails subtly on Mac when we force embedding, so I've
#ifdef'd that away.  Other platforms look fine.

BUG=skia:

Review URL: https://codereview.chromium.org/796523002