add a new hsl GM

Change-Id: I2c8b9df3e6bf40de4b38966fa8ea671fc68aa45f
Reviewed-on: https://skia-review.googlesource.com/15635
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/gn/gm.gni b/gn/gm.gni
index eb81887..a14c2eb 100644
--- a/gn/gm.gni
+++ b/gn/gm.gni
@@ -149,6 +149,7 @@
   "$_gm/hardstop_gradients.cpp",
   "$_gm/highcontrastfilter.cpp",
   "$_gm/hittestpath.cpp",
+  "$_gm/hsl.cpp",
   "$_gm/image.cpp",
   "$_gm/image_pict.cpp",
   "$_gm/image_shader.cpp",