Replace make_RGBW_shader shader with a gradient.

This is functionally the same, but will work in Graphite without
special bitmap handling. Also, this change exposed a bug in the
blender tests--the code was evaluating the edges between pixels,
instead of pixel centers.

Change-Id: I4c152b019812a5572dea0de5cb223bc1d0ba0ead
Commit-Queue: Michael Ludwig <>
Reviewed-by: Michael Ludwig <>
Auto-Submit: John Stiles <>
2 files changed