Add the download component and initial setup

chrome/browser/BUILD.gn

Index: chrome/browser/BUILD.gn
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 500769dd5cee27051dc50a88990a40d9477ac42f..c579c052dc7afc1a4e2bae2766d30a4633f9c18b 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -350,6 +350,8 @@ split_static_library("browser") {
     "download/download_request_limiter.h",
     "download/download_resource_throttle.cc",
     "download/download_resource_throttle.h",
+    "download/download_service_factory.cc",
+    "download/download_service_factory.h",
     "download/download_started_animation.h",
     "download/download_stats.cc",
     "download/download_stats.h",
@@ -1479,6 +1481,7 @@ split_static_library("browser") {
     "//components/dom_distiller/content/browser",
     "//components/domain_reliability",
     "//components/doodle",
+    "//components/download",
     "//components/error_page/common",
     "//components/favicon/content",
     "//components/favicon/core",