Emit dumpInfo string when processor opt test fails

Add missing implementation for ComposeTwo, and provide more information in
ComposeOne.

BUG=skia:

Change-Id: Id2406bcb51a6419a763ff9e6e572f5c6c70c4c76
Reviewed-on: https://skia-review.googlesource.com/9699
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed