Revert of Remove enable_topchrome_md build flag

tools/grit/grit_rule.gni

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Instantiate grit. This will produce a script target to run grit, and a
 # static library that compiles the .cc files.
 #
 # Parameters
 #
 #   source (required)
@@ skipping 287 matching lines @@
     "-D",
     "enable_service_discovery",
   ]
 }
 if (mac_views_browser) {
   grit_defines += [
     "-D",
     "mac_views_browser",
   ]
 }
+if (enable_topchrome_md) {
+  grit_defines += [
+    "-D",
+    "enable_topchrome_md",
+  ]
+}
 
 grit_resource_id_file = "//tools/gritsettings/resource_ids"
 grit_info_script = "//tools/grit/grit_info.py"
 
 template("grit") {
   assert(defined(invoker.source),
          "\"source\" must be defined for the grit template $target_name")
 
   grit_inputs = [ invoker.source ]
 
@@ skipping 174 matching lines @@
     if (defined(invoker.configs)) {
       configs += invoker.configs
     }
 
     if (defined(invoker.visibility)) {
       visibility = invoker.visibility
     }
     output_name = grit_output_name
   }
 }