DM: track a direct/indirect bit for each Sink too.

The decoding tests can now veto indirect sinks like pipe-8888.

This moves Sink type detection from automatic to explicit; I can't think of any
way to automatically differentiate pipe-8888 from 8888 based only on the
output.  (They should ideally be identical, after all.)

BUG=skia:4138

Review URL: https://codereview.chromium.org/1263113002
3 files changed