Put more files under the enable_service_discovery build flag.

chrome/browser/extensions/BUILD.gn

 # 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.
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 
 assert(enable_extensions)
 
 gypi_values =
@@ skipping 100 matching lines @@
     }
   }
 
   if (!is_android) {
     sources +=
         rebase_path(gypi_values.chrome_browser_extensions_non_android_sources,
                     ".",
                     "//chrome")
   }
 
+  if (enable_service_discovery) {
+    sources += rebase_path(
+            gypi_values.chrome_browser_extensions_service_discovery_sources,
+            ".",
+            "//chrome")
+  }
+
   if (use_ash) {
     sources += [
       "api/tabs/ash_panel_contents.cc",
       "api/tabs/ash_panel_contents.h",
     ]
   }
 
   if (use_aura) {
     deps += [
       "//ui/keyboard",
@@ skipping 83 matching lines @@
                     "//chrome")
   }
 
   if (is_chromeos && use_ozone) {
     sources -= [ "global_shortcut_listener_chromeos.cc" ]
   }
   if (!use_ozone) {
     sources -= [ "global_shortcut_listener_ozone.cc" ]
   }
 }