Initial checkin of new SkSL interpreter.

Not quite feature complete yet, but at a point where it's worth checking
in.

Bug: skia:
Change-Id: I21141d30e8582a79e94450d84e56bacc067249e0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/201685
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/gn/tests.gni b/gn/tests.gni
index 14738e3..3ec84ec 100644
--- a/gn/tests.gni
+++ b/gn/tests.gni
@@ -239,6 +239,7 @@
   "$_tests/SkSLErrorTest.cpp",
   "$_tests/SkSLFPTest.cpp",
   "$_tests/SkSLGLSLTest.cpp",
+  "$_tests/SkSLInterpreterTest.cpp",
   "$_tests/SkSLJITTest.cpp",
   "$_tests/SkSLMemoryLayoutTest.cpp",
   "$_tests/SkSLMetalTest.cpp",