manually register codecs in DM

We'll want to do this when we've got Google3 refactored
to slice out each of these four codecs into its own little target.

Small tweaks to make SkPngCodec match the pattern of the rest.

Should be harmless to have both the compile-time and runtime
registration, right?

Change-Id: Ic72394764ac267758dc1023e85f3d0c4b655d420
Reviewed-by: Brian Osman <>
Commit-Queue: Mike Klein <>
3 files changed