Recent changes (crrev.com/2045293002) made it so that a GIF may not
support index 8. In that case, make SkAndroidCodec not suggest index 8.
Add a test and a new test file. randPixelsOffset.gif is the same as
randPixels.gif, except its frame is offset. Since it does not have a
transparent index, we have to decode to kN32.
Change-Id: I1c09ab9094083de3dfc436632b3c26dbde1dccbd
Reviewed-on: https://skia-review.googlesource.com/6196
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Matt Sarett <msarett@google.com>
