Downloads: replace BrowserThread::FILE with task scheduler.

content/public/browser/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/ui.gni")
 
 # See //content/BUILD.gn for how this works.
 group("browser") {
   if (is_component_build) {
     public_deps = [
@@ skipping 86 matching lines @@
     "devtools_external_agent_proxy_delegate.h",
     "devtools_frontend_host.h",
     "devtools_manager_delegate.cc",
     "devtools_manager_delegate.h",
     "devtools_socket_factory.h",
     "dom_storage_context.h",
     "download_danger_type.h",
     "download_interrupt_reason_values.h",
     "download_interrupt_reasons.h",
     "download_item.h",
+    "download_manager.cc",
     "download_manager.h",
     "download_manager_delegate.cc",
     "download_manager_delegate.h",
     "download_save_info.cc",
     "download_save_info.h",
     "download_url_parameters.cc",
     "download_url_parameters.h",
     "favicon_status.cc",
     "favicon_status.h",
     "file_descriptor_info.h",
@@ skipping 238 matching lines @@
     ]
   }
 
   if (is_chromeos) {
     sources += [
       "arc_tracing_agent.cc",
       "arc_tracing_agent.h",
     ]
   }
 }