Test a GIF with an out of range transparent index

Bug: skia:8461

According to skbug.com/7069, we should allow GIFs to use a transparent
index outside of the range of the color table. Add a test to verify
support for this.

The GIF is 2x2 with the following pixels:
|   black            |          white           |
|   transparent      |      transparent         |

The color table only has 2 entries (black and white), and the
transparent index is 2.

Change-Id: I16574a61e2982b6628c3eca96cb7b3e1f57d3b2a
Reviewed-on: https://skia-review.googlesource.com/c/161561
Reviewed-by: Nigel Tao <nigeltao@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
Auto-Submit: Leon Scroggins <scroggo@google.com>
1 file changed