Change SampleMatrix to SampleUsage

It now tracks all sample calls of a child (matrix, explicit coords,
pass through). There is now just one registerChild() call, and the
sampling pattern of that child is fully determined by the SampleUsage
parameter.

Change-Id: Iaadcd325fca64a59f24192aadd06923c66362181
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/299875
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/src/gpu/effects/GrGaussianConvolutionFragmentProcessor.cpp b/src/gpu/effects/GrGaussianConvolutionFragmentProcessor.cpp
index a8ab80a..55fe393 100644
--- a/src/gpu/effects/GrGaussianConvolutionFragmentProcessor.cpp
+++ b/src/gpu/effects/GrGaussianConvolutionFragmentProcessor.cpp
@@ -169,7 +169,7 @@
                     ProcessorOptimizationFlags(child.get()))
         , fRadius(radius)
         , fDirection(direction) {
-    this->registerExplicitlySampledChild(std::move(child));
+    this->registerChild(std::move(child), SkSL::SampleUsage::Explicit());
     SkASSERT(radius <= kMaxKernelRadius);
     fill_in_1D_gaussian_kernel(fKernel, gaussianSigma, fRadius);
     this->setUsesSampleCoordsDirectly();