Remove prerender cookie store, part 4.

This removes the ability to pass in a custom CookieStore to a URLRequest. It's
a small change to net/url_request which then balloons to everything in the
project that ever makes a URLRequest.

This reverts the rest of https://codereview.chromium.org/188693003 (and then
does a whole lot more because URLRequest constructors were unified recently to
always require passing in the fourth argument).

BUG=457344

Review URL: https://codereview.chromium.org/1003953008

Cr-Commit-Position: refs/heads/master@{#321820}
diff --git a/content/browser/download/download_manager_impl.cc b/content/browser/download/download_manager_impl.cc
index bdb820b4..ce39612f 100644
--- a/content/browser/download/download_manager_impl.cc
+++ b/content/browser/download/download_manager_impl.cc
@@ -56,7 +56,7 @@
   // we must down cast. RDHI is the only subclass of RDH as of 2012 May 4.
   scoped_ptr<net::URLRequest> request(
       params->resource_context()->GetRequestContext()->CreateRequest(
-          params->url(), net::DEFAULT_PRIORITY, NULL, NULL));
+          params->url(), net::DEFAULT_PRIORITY, NULL));
   request->set_method(params->method());
   if (!params->post_body().empty()) {
     const std::string& body = params->post_body();