In FPs, store pointers for all child slots, even nullptr

This simplifies things like ConstantOutputForConstantInput and
invokeChild. It also removes the need for child indices: generated
FPs now directly refer to their children by slot number.

Change-Id: I69bbb042d5d72d21b999256f969c467702d0774d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/302436
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
diff --git a/src/gpu/gradients/generated/GrRadialGradientLayout.cpp b/src/gpu/gradients/generated/GrRadialGradientLayout.cpp
index 602a648..2cc1d47 100644
--- a/src/gpu/gradients/generated/GrRadialGradientLayout.cpp
+++ b/src/gpu/gradients/generated/GrRadialGradientLayout.cpp
@@ -46,6 +46,7 @@
 }
 GrRadialGradientLayout::GrRadialGradientLayout(const GrRadialGradientLayout& src)
         : INHERITED(kGrRadialGradientLayout_ClassID, src.optimizationFlags()) {
+    this->cloneAndRegisterAllChildProcessors(src);
     this->setUsesSampleCoordsDirectly();
 }
 std::unique_ptr<GrFragmentProcessor> GrRadialGradientLayout::clone() const {