Enable sandbox in local discovery utility process.

chrome/utility/chrome_content_utility_client.cc

Index: chrome/utility/chrome_content_utility_client.cc
diff --git a/chrome/utility/chrome_content_utility_client.cc b/chrome/utility/chrome_content_utility_client.cc
index 967352b6ca42ebae43d52b012e844d01f1134af7..b5db0fd7eb1b5f95eadc6b500e5e45571241d3e6 100644
--- a/chrome/utility/chrome_content_utility_client.cc
+++ b/chrome/utility/chrome_content_utility_client.cc
@@ -151,6 +151,12 @@ bool ChromeContentUtilityClient::OnMessageReceived(
   return handled;
 }
 
+void ChromeContentUtilityClient::PreSandboxStartup() {
+#if defined(ENABLE_MDNS)
+  local_discovery::ServiceDiscoveryMessageHandler::PreSandboxStartup();
+#endif  // ENABLE_MDNS
+}
+
 void ChromeContentUtilityClient::OnUnpackExtension(
     const base::FilePath& extension_path,
     const std::string& extension_id,