Add SkNVRefCnt, prune down SkPicture's size

SkNVRefCnt is a variant of SkRefCnt that's Not Virtual, so weighs 4 bytes
instead of 8 or 16.  There's only benefit to doing this if the deriving class
does not otherwise need a vtable, e.g. SkPicture.

I've stripped out some cruft from SkPicture, rearranged fields to pack tightly,
and added compile asserts for the sizes of SkPicture, SkRecord, and
SkVarAlloc.

BUG=skia:3144

Review URL: https://codereview.chromium.org/741793002

0 files changed, 0 insertions, 0 deletions