Update from https://crrev.com/312398

net/BUILD.gn

Index: net/BUILD.gn
diff --git a/net/BUILD.gn b/net/BUILD.gn
index aa9f7023bf5f33c38c8a76f979a6acdb86585278..cc95c2b77e355f5973b449b8263b8b39565079cc 100644
--- a/net/BUILD.gn
+++ b/net/BUILD.gn
@@ -7,6 +7,7 @@ import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build/module_args/v8.gni")
 import("//url/config.gni")
+import("//testing/test.gni")
 
 # TODO(cjhopman): //build/config/android/rules.gni also imports grit_rule.gni.
 # Currently, that file can't be imported multiple times.  Make this always
@@ -684,6 +685,8 @@ source_set("test_support") {
     "test/url_request/url_request_mock_data_job.h",
     "test/url_request/url_request_mock_http_job.cc",
     "test/url_request/url_request_mock_http_job.h",
+    "test/url_request/url_request_slow_download_job.cc",
+    "test/url_request/url_request_slow_download_job.h",
     "url_request/test_url_fetcher_factory.cc",
     "url_request/test_url_fetcher_factory.h",
     "url_request/test_url_request_interceptor.cc",