add print to pdf for headless

content/public/browser/devtools_manager_delegate.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 "content/public/browser/devtools_agent_host.h"
 #include "content/public/browser/devtools_manager_delegate.h"
 
 namespace content {
 
 void DevToolsManagerDelegate::Inspect(DevToolsAgentHost* agent_host) {
@@ skipping 21 matching lines @@
     const GURL& url) {
   return nullptr;
 }
 
 base::DictionaryValue* DevToolsManagerDelegate::HandleCommand(
       DevToolsAgentHost* agent_host,
       base::DictionaryValue* command) {
   return nullptr;
 }
 
-bool DevToolsManagerDelegate::HandleAsyncCommand(DevToolsAgentHost* agent_host,
-                                                 base::DictionaryValue* command,
-                                                 CommandCallback callback) {
+bool DevToolsManagerDelegate::HandleAsyncCommand(
+    DevToolsAgentHost* agent_host,
+    base::DictionaryValue* command,
+    const CommandCallback& callback) {
   return false;
 }
 
 std::string DevToolsManagerDelegate::GetDiscoveryPageHTML() {
   return std::string();
 }
 
 std::string DevToolsManagerDelegate::GetFrontendResource(
     const std::string& path) {
   return std::string();
 }
 
 DevToolsManagerDelegate::~DevToolsManagerDelegate() {
 }
 
 }  // namespace content