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/effects/generated/GrCircleEffect.cpp b/src/gpu/effects/generated/GrCircleEffect.cpp
index f9df3c9..f90c8f7 100644
--- a/src/gpu/effects/generated/GrCircleEffect.cpp
+++ b/src/gpu/effects/generated/GrCircleEffect.cpp
@@ -49,12 +49,7 @@
                 args.fUniformHandler->getUniformCStr(circleVar),
                 args.fUniformHandler->getUniformCStr(circleVar));
         SkString _input2509(args.fInputColor);
-        SkString _sample2509;
-        if (_outer.inputFP_index >= 0) {
-            _sample2509 = this->invokeChild(_outer.inputFP_index, _input2509.c_str(), args);
-        } else {
-            _sample2509.swap(_input2509);
-        }
+        SkString _sample2509 = this->invokeChild(0, _input2509.c_str(), args);
         fragBuilder->codeAppendf(
                 R"SkSL(
 half4 inputColor = %s;
@@ -121,9 +116,7 @@
         , edgeType(src.edgeType)
         , center(src.center)
         , radius(src.radius) {
-    if (src.inputFP_index >= 0) {
-        inputFP_index = this->cloneAndRegisterChildProcessor(src.childProcessor(src.inputFP_index));
-    }
+    this->cloneAndRegisterAllChildProcessors(src);
 }
 std::unique_ptr<GrFragmentProcessor> GrCircleEffect::clone() const {
     return std::unique_ptr<GrFragmentProcessor>(new GrCircleEffect(*this));