Add pending preloads indexed by routing id. Start preloading once we navigate.

content/browser/renderer_host/resource_dispatcher_host.cc

Index: content/browser/renderer_host/resource_dispatcher_host.cc
diff --git a/content/browser/renderer_host/resource_dispatcher_host.cc b/content/browser/renderer_host/resource_dispatcher_host.cc
index aebdbb045e7a7e7503d95e542fcce1b5383f1501..f65b825dda444f986de94f3f2c7c4ddbe0c390bf 100644
--- a/content/browser/renderer_host/resource_dispatcher_host.cc
+++ b/content/browser/renderer_host/resource_dispatcher_host.cc
@@ -467,9 +467,9 @@ void ResourceDispatcherHost::BeginRequest(
   // but after the BufferedResourceHandler since it depends on the MIME
   // sniffing capabilities in the BufferedResourceHandler.
   prerender::PrerenderResourceHandler* pre_handler =
-      prerender::PrerenderResourceHandler::MaybeCreate(*request,
-                                                       context,
-                                                       handler);
+      prerender::PrerenderResourceHandler::MaybeCreate(
+          *request, context, handler, ((load_flags & net::LOAD_PRERENDER) != 0),
+          child_id, route_id);
   if (pre_handler)
     handler = pre_handler;