Make enable_service_discovery a chrome/ feature.

chrome/app/BUILD.gn

Index: chrome/app/BUILD.gn
diff --git a/chrome/app/BUILD.gn b/chrome/app/BUILD.gn
index ece858cf95a29ad022d081357677be418f67501e..bbaaeada7f5c299644d64c1b2d385e68f1d8c005 100644
--- a/chrome/app/BUILD.gn
+++ b/chrome/app/BUILD.gn
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/ui.gni")
+import("//chrome/common/features.gni")
 import("//services/shell/public/service_manifest.gni")
 import("//tools/grit/grit_rule.gni")
 
@@ -79,6 +80,7 @@ if (is_android) {
 grit("generated_resources") {
   source = "generated_resources.grd"
   use_qualified_include = true
+  defines = chrome_grit_defines
   output_dir = "$root_gen_dir/chrome"
   outputs = [
     "grit/generated_resources.h",