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/gn/sksl.gni b/gn/sksl.gni
index b769188..aa80bd7 100644
--- a/gn/sksl.gni
+++ b/gn/sksl.gni
@@ -8,7 +8,7 @@
 _include = get_path_info("../include", "abspath")
 
 skia_sksl_sources = [
-  "$_include/private/SkSLSampleMatrix.h",
+  "$_include/private/SkSLSampleUsage.h",
   "$_src/sksl/SkSLASTFile.h",
   "$_src/sksl/SkSLASTNode.cpp",
   "$_src/sksl/SkSLASTNode.h",
@@ -36,7 +36,7 @@
   "$_src/sksl/SkSLParser.cpp",
   "$_src/sksl/SkSLParser.h",
   "$_src/sksl/SkSLPosition.h",
-  "$_src/sksl/SkSLSampleMatrix.cpp",
+  "$_src/sksl/SkSLSampleUsage.cpp",
   "$_src/sksl/SkSLSectionAndParameterHelper.cpp",
   "$_src/sksl/SkSLSectionAndParameterHelper.h",
   "$_src/sksl/SkSLString.cpp",