headless: Add support for host resolver mapping

headless/public/headless_browser.h

Index: headless/public/headless_browser.h
diff --git a/headless/public/headless_browser.h b/headless/public/headless_browser.h
index a04b2e573045ccb9d0cc02a438ab064eb1aa03f2..ef323436ab13cea0cdc745a162f9cff7d6aa6423 100644
--- a/headless/public/headless_browser.h
+++ b/headless/public/headless_browser.h
@@ -87,6 +87,10 @@ struct HeadlessBrowser::Options {
   // web content, which can be a security risk.
   bool single_process_mode;
 
+  // Comma-separated list of rules that control how hostnames are mapped. See
+  // chrome::switches::kHostRules for a description for the format.
+  std::string host_resolver_rules;
+
  private:
   Options(int argc, const char** argv);
 };
@@ -102,6 +106,7 @@ class HeadlessBrowser::Options::Builder {
   Builder& SetMessagePump(base::MessagePump* message_pump);
   Builder& SetProxyServer(const net::HostPortPair& proxy_server);
   Builder& SetSingleProcessMode(bool single_process_mode);
+  Builder& SetHostResolverRules(const std::string& host_resolver_rules);
 
   Options Build();