rename new GM

Our new srgb_color_filter (in gm/srgb_color_filter.cpp) is awfully
similar to the existing srgb_colorfilter (in gm/srgb.cpp).

Let's rename the new one.

Change-Id: I8c7816c377cc4342388be51632353882a1bc5241
Reviewed-on: https://skia-review.googlesource.com/26525
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/gn/gm.gni b/gn/gm.gni
index 97f8d83..8728b5a 100644
--- a/gn/gm.gni
+++ b/gn/gm.gni
@@ -277,7 +277,7 @@
   "$_gm/spritebitmap.cpp",
   "$_gm/srcmode.cpp",
   "$_gm/srgb.cpp",
-  "$_gm/srgb_color_filter.cpp",
+  "$_gm/tosrgb_colorfilter.cpp",
   "$_gm/stlouisarch.cpp",
   "$_gm/stringart.cpp",
   "$_gm/stroke_rect_shader.cpp",