Convert GN visibility variables to lists.

build/secondary/tools/grit/grit_rule.gni

Index: build/secondary/tools/grit/grit_rule.gni
diff --git a/build/secondary/tools/grit/grit_rule.gni b/build/secondary/tools/grit/grit_rule.gni
index bec147eebbecae844039d305e1600567a0c1040b..4cffc4ee935320a22e92672bf0373a7a79ccae84 100644
--- a/build/secondary/tools/grit/grit_rule.gni
+++ b/build/secondary/tools/grit/grit_rule.gni
@@ -258,7 +258,7 @@ template("grit") {
   # The config and the action below get this visibility son only the generated
   # source set can depend on them. The variable "target_name" will get
   # overwritten inside the inner classes so we need to compute it here.
-  target_visibility = ":$target_name"
+  target_visibility = [ ":$target_name" ]
 
   # The current grit setup makes an file in $output_dir/grit/foo.h that
   # the source code expects to include via "grit/foo.h". It would be nice to
@@ -301,7 +301,16 @@ template("grit") {
 
     args += grit_flags + assert_files_flags
 
-    visibility = target_visibility
+    if (defined(invoker.visibility)) {
+      # This needs to include both what the invoker specified (since they
+      # probably include generated headers from this target), as well as the
+      # generated source set (since there's no guarantee that the visibility
+      # specified by the invoker includes our target).
+      #
+      # Only define visibility at all if the invoker specified it. Otherwise,
+      # we want to keep the public "no visibility specified" default.
+      visibility = target_visibility + invoker.visibility
+    }
 
     deps = [ "//tools/grit:grit_sources" ]
     if (defined(invoker.deps)) {