headless: Switch to multiprocess mode by default

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 5e284968762083475fe62aaeb77b5bc4a252494b..de5f89bd3efe16457627eca07e5241876f3799c0 100644
--- a/headless/public/headless_browser.h
+++ b/headless/public/headless_browser.h
@@ -90,6 +90,11 @@ struct HeadlessBrowser::Options {
   // chrome::switches::kHostRules for a description for the format.
   std::string host_resolver_rules;
 
+  // Run the browser in single process mode instead of using separate renderer
+  // processes as per default. Note that this also disables any sandboxing of
+  // web content, which can be a security risk.
+  bool single_process_mode;
+
  private:
   Options(int argc, const char** argv);
 };
@@ -105,6 +110,7 @@ class HeadlessBrowser::Options::Builder {
   Builder& SetMessagePump(base::MessagePump* message_pump);
   Builder& SetProxyServer(const net::HostPortPair& proxy_server);
   Builder& SetHostResolverRules(const std::string& host_resolver_rules);
+  Builder& SetSingleProcessMode(bool single_process_mode);
 
   Options Build();