Use TaskScheduler instead of WorkerPool in extension_printer_handler.cc.

chrome/browser/ui/webui/print_preview/printer_handler.cc

 // Copyright 2015 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_handler.h"
 
-#include "base/threading/worker_pool.h"
 #include "chrome/browser/ui/webui/print_preview/extension_printer_handler.h"
 
 // static
 std::unique_ptr<PrinterHandler> PrinterHandler::CreateForExtensionPrinters(
     content::BrowserContext* browser_context) {
-  return std::unique_ptr<ExtensionPrinterHandler>(new ExtensionPrinterHandler(
-      browser_context, base::WorkerPool::GetTaskRunner(true)));
+  return std::unique_ptr<ExtensionPrinterHandler>(
+      new ExtensionPrinterHandler(browser_context));
 }