headless: Add a dedicated child process entrypoint

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 <iostream>
 #include <memory>
 #include <string>
 
 #include "base/base64.h"
 #include "base/bind.h"
@@ skipping 267 matching lines @@
   HeadlessBrowser* browser_;  // Not owned.
   std::unique_ptr<HeadlessDevToolsClient> devtools_client_;
   HeadlessWebContents* web_contents_;
   bool processed_page_ready_;
   std::unique_ptr<net::FileStream> screenshot_file_stream_;
 
   DISALLOW_COPY_AND_ASSIGN(HeadlessShell);
 };
 
 int main(int argc, const char** argv) {
+  headless::RunChildProcessIfNeeded(argc, argv);
   HeadlessShell shell;
   HeadlessBrowser::Options::Builder builder(argc, argv);
 
   // Enable devtools if requested.
   base::CommandLine command_line(argc, argv);
   if (command_line.HasSwitch(switches::kRemoteDebuggingPort)) {
     std::string address = kDevToolsHttpServerAddress;
     if (command_line.HasSwitch(headless::switches::kRemoteDebuggingAddress)) {
       address = command_line.GetSwitchValueASCII(
           headless::switches::kRemoteDebuggingAddress);
@@ skipping 32 matching lines @@
 
   if (command_line.HasSwitch(switches::kHostResolverRules)) {
     builder.SetHostResolverRules(
         command_line.GetSwitchValueASCII(switches::kHostResolverRules));
   }
 
   return HeadlessBrowserMain(
       builder.Build(),
       base::Bind(&HeadlessShell::OnStart, base::Unretained(&shell)));
 }