Add helper method to clone and register a child FP.

This will remove common boilerplate from our gen-code, and gives us a
place to put common child-cloning boilerplate.

Change-Id: I6101655af89d4c5844ec908b81ce4f6e5d59f834
Bug: skia:10217
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/296177
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
diff --git a/src/gpu/effects/generated/GrDeviceSpaceEffect.cpp b/src/gpu/effects/generated/GrDeviceSpaceEffect.cpp
index 3832502..8ae5c9f 100644
--- a/src/gpu/effects/generated/GrDeviceSpaceEffect.cpp
+++ b/src/gpu/effects/generated/GrDeviceSpaceEffect.cpp
@@ -58,13 +58,7 @@
 }
 GrDeviceSpaceEffect::GrDeviceSpaceEffect(const GrDeviceSpaceEffect& src)
         : INHERITED(kGrDeviceSpaceEffect_ClassID, src.optimizationFlags()), matrix(src.matrix) {
-    {
-        auto fp_clone = src.childProcessor(src.fp_index).clone();
-        if (src.childProcessor(src.fp_index).isSampledWithExplicitCoords()) {
-            fp_clone->setSampledWithExplicitCoords();
-        }
-        fp_index = this->registerChildProcessor(std::move(fp_clone));
-    }
+    { fp_index = this->cloneAndRegisterChildProcessor(src.childProcessor(src.fp_index)); }
 }
 std::unique_ptr<GrFragmentProcessor> GrDeviceSpaceEffect::clone() const {
     return std::unique_ptr<GrFragmentProcessor>(new GrDeviceSpaceEffect(*this));