Tweak viewer's shader panel

Base the box size on the shader length (within reason).

Change-Id: If847cb4de0cea3cb2267f284fd5bbb653f25e185
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/311455
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed