unbundle: add //services/data_decoder:lib to libxml_utils visibility

Also add a note to keep original and unbundle BUILD.gn files in sync.

Bug: 1306942
Change-Id: I83a57abfd7f2390232b1cf81060d79595f2aec55
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3488058
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Stephan Hartmann <stha09@googlemail.com>
Cr-Commit-Position: refs/heads/main@{#995726}
NOKEYCHECK=True
GitOrigin-RevId: e67b31a6d61ec67c3cd89832a96e266f3470b5f0
diff --git a/BUILD.gn b/BUILD.gn
index 24688c1..f408123 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -75,6 +75,7 @@
   }
 }
 
+# Please keep in sync with //build/linux/unbundle/libxml.gn.
 static_library("xml_reader") {
   # Do not expand this visibility list without first consulting with the
   # Security Team.
@@ -98,6 +99,7 @@
   configs += [ ":libxml_config" ]
 }
 
+# Please keep in sync with //build/linux/unbundle/libxml.gn.
 static_library("xml_writer") {
   # The XmlWriter is considered safe to use from any target.
   visibility = [ "*" ]
@@ -112,6 +114,7 @@
   configs += [ ":libxml_config" ]
 }
 
+# Please keep in sync with //build/linux/unbundle/libxml.gn.
 static_library("libxml_utils") {
   # Do not expand this visibility list without first consulting with the
   # Security Team.