Introduce GN to desktop_linux arg and grit_defines list.

tools/gn/secondary/tools/grit/grit_rule.gni

Index: tools/gn/secondary/tools/grit/grit_rule.gni
diff --git a/tools/gn/secondary/tools/grit/grit_rule.gni b/tools/gn/secondary/tools/grit/grit_rule.gni
index 31307e4184471b0087932d7cf601b412d1d3e88a..cec42cb35316408cdec8b1fc61ebfeddddd9210f 100644
--- a/tools/gn/secondary/tools/grit/grit_rule.gni
+++ b/tools/gn/secondary/tools/grit/grit_rule.gni
@@ -12,6 +12,7 @@
 #     # You can also put deps here if the grit source depends on generated
 #     # files.
 #   }
+import ("//build/config/ui.gni")
 template("grit") {
   assert(defined(invoker.source),
          "\"source\" must be defined for the grit template $target_name")
@@ -75,7 +76,7 @@ template("grit") {
       "-i", source_path, "build",
       "-f", resource_ids,
       "-o", output_dir,
-    ] + grit_flags
+    ] + grit_defines + grit_flags
 
     visibility = target_visibility
   }