Restructure null-child test to avoid two-argument Runtime Shader.

The two-argument Runtime Shader is set for deprecation, so let's
keep it out of our test cases.

The test code is also more explicit now about where the paint color
does and does not contribute, and sets bogus non-contributing paint
colors to demonstrate that it isn't used.

Change-Id: I7a60d22c9a2f31ac0864eead1cd227a17b2faec4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/580419
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
1 file changed