Add SkCodec::Result indicating error in the data

Previously, SkGifCodec treated an error in the LZW data as incomplete,
since we can still draw the partially decoded image. But a client doing
incremental decodes needs to distinguish this from truly incomplete
data. In the case of an error, the client should not attempt to provide
more data and decode again.

Add kErrorInInput, and return it when SkGifCodec sees a fatal error.
Treat it the same as kIncompleteInput when it comes to filling and DM.

Bug: skia:6825
Change-Id: Ic6ce3a62c0b065ed34dcd8006309e43272a3db9f
Reviewed-on: https://skia-review.googlesource.com/21530
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Chris Blume <cblume@chromium.org>
8 files changed