Revert of Remove enable_topchrome_md build flag

build/config/BUILD.gn

 # Copyright (c) 2013 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.
 
 import("//build/config/allocator.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/features.gni")
@@ skipping 186 matching lines @@
   }
   if (enable_supervised_users) {
     defines += [ "ENABLE_SUPERVISED_USERS=1" ]
   }
   if (enable_service_discovery) {
     defines += [ "ENABLE_SERVICE_DISCOVERY=1" ]
   }
   if (enable_image_loader_extension) {
     defines += [ "IMAGE_LOADER_EXTENSION=1" ]
   }
+  if (enable_topchrome_md) {
+    defines += [ "ENABLE_TOPCHROME_MD=1" ]
+  }
   if (enable_wayland_server) {
     defines += [ "ENABLE_WAYLAND_SERVER=1" ]
   }
   if (enable_wifi_display) {
     defines += [ "ENABLE_WIFI_DISPLAY=1" ]
   }
   if (proprietary_codecs) {
     defines += [ "USE_PROPRIETARY_CODECS" ]
   }
   if (enable_hangout_services_extension) {
@@ skipping 224 matching lines @@
       # file doesn't exist, no error will be generated (probably MS tested this
       # case but forgot the other one?). To reproduce this error, do a build,
       # then delete the precompile.c.obj file, then build again.
       cflags_c = [ "/wd4206" ]
     } else if (is_mac) {
       precompiled_header = "build/precompile.h"
       precompiled_source = "//build/precompile.h"
     }
   }
 }