headless: Add support for host resolver mapping

headless/app/headless_shell.cc

 // Copyright 2016 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.
 
 #include <memory>
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/location.h"
@@ skipping 109 matching lines @@
         command_line.GetSwitchValueASCII(headless::switches::kProxyServer);
     net::HostPortPair parsed_proxy_server =
         net::HostPortPair::FromString(proxy_server);
     if (parsed_proxy_server.host().empty() || !parsed_proxy_server.port()) {
       LOG(ERROR) << "Malformed proxy server url";
       return EXIT_FAILURE;
     }
     builder.SetProxyServer(parsed_proxy_server);
   }
 
+  if (command_line.HasSwitch(switches::kHostResolverRules)) {
+    builder.SetHostResolverRules(
+        command_line.GetSwitchValueASCII(switches::kHostResolverRules));
+  }
+
   return HeadlessBrowserMain(
       builder.Build(),
       base::Bind(&HeadlessShell::OnStart, base::Unretained(&shell)));
 }