Revert "Revert "Initial checkin of SkSL lexical analyzer generator (not actually in use yet).""

This reverts commit 3ed4781ee1bd5af9b3ee2623e5356e86ce36e812.

Bug: skia:
Change-Id: If0de7ca17c4da8000d3526a73b71be6ee34ce060
Reviewed-on: https://skia-review.googlesource.com/43561
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 4b34a6d..1c328b0 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -412,6 +412,16 @@
 }
 
 if (skia_compile_processors) {
+  executable("sksllex") {
+    sources = [
+      "src/sksl/lex/Main.cpp",
+      "src/sksl/lex/NFA.cpp",
+      "src/sksl/lex/RegexNode.cpp",
+      "src/sksl/lex/RegexParser.cpp",
+    ]
+    include_dirs = [ "src/sksl/lex" ]
+  }
+
   executable("skslc") {
     defines = [ "SKSL_STANDALONE" ]
     sources = [