Add sample(child, matrix) to SkSL.

This allows fragment processors to sample their children with their
local coordinate system transformed by a matrix.

Change-Id: Ifa848bbd85b939bbc5751fec5cf8f89ee904bf39
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/282590
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
diff --git a/src/gpu/effects/GrGaussianConvolutionFragmentProcessor.cpp b/src/gpu/effects/GrGaussianConvolutionFragmentProcessor.cpp
index 0488518..118efe8 100644
--- a/src/gpu/effects/GrGaussianConvolutionFragmentProcessor.cpp
+++ b/src/gpu/effects/GrGaussianConvolutionFragmentProcessor.cpp
@@ -56,7 +56,8 @@
                                                  "Kernel", arrayCount);
 
     GrGLSLFPFragmentBuilder* fragBuilder = args.fFragBuilder;
-    SkString coords2D = fragBuilder->ensureCoords2D(args.fTransformedCoords[0].fVaryingPoint);
+    SkString coords2D = fragBuilder->ensureCoords2D(args.fTransformedCoords[0].fVaryingPoint,
+                                                    ce.sampleMatrix());
 
     fragBuilder->codeAppendf("%s = half4(0, 0, 0, 0);", args.fOutputColor);