Add missing #include around sequenced_worker_pool.h in //chrome

chrome/browser/ui/webui/print_preview/printer_capabilities.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 "chrome/browser/ui/webui/print_preview/printer_capabilities.h"
 
 #include <memory>
 #include <string>
 #include <utility>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/stl_util.h"
 #include "base/strings/string_piece.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "base/values.h"
 #include "chrome/common/cloud_print/cloud_print_cdd_conversion.h"
 #include "chrome/common/crash_keys.h"
 #include "content/public/browser/browser_thread.h"
 #include "printing/backend/print_backend.h"
 #include "printing/backend/print_backend_consts.h"
 
 namespace printing {
 
 const char kPrinterId[] = "printerId";
@@ skipping 77 matching lines @@
 
   auto capabilities = GetPrinterCapabilitiesOnBlockingPoolThread(device_name);
   if (!capabilities)
     capabilities = base::MakeUnique<base::DictionaryValue>();
   printer_info->Set(kPrinterCapabilities, std::move(capabilities));
 
   return printer_info;
 }
 
 }  // namespace printing