Avoid recomputing the input texel colors in Processor tests.

Profiling showed that repeated calls to `input_texel_color` were
actually a very expensive part of the test. Fortunately, we can expose
the texture's pixel buffer to the unit test method and easily reclaim
that performance.

Change-Id: I2c1cdd57a3e14dc859bdf03d8131137ca81364ff
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/309437
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
1 file changed