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 ce7548176b975c5f49067d7ca024a882a4f1ae13..823110a92f93d167cdcb44b3421a2306e74486a7 100644
--- a/content/browser/renderer_host/resource_dispatcher_host.cc
+++ b/content/browser/renderer_host/resource_dispatcher_host.cc
@@ -468,10 +468,13 @@ void ResourceDispatcherHost::BeginRequest(
   // be prerendered. This should be in front of the [a]syncResourceHandler,
   // but after the BufferedResourceHandler since it depends on the MIME
   // sniffing capabilities in the BufferedResourceHandler.
+  bool is_from_prerender = ((load_flags & net::LOAD_PRERENDER) != 0);

[cbentzel, 2011/03/14 14:05:55]

It seems like this CL would be a lot simpler if you simply skipped MaybeCreate
in this case, or failed internally in MaybeCreate. 

Why would we try to create a Prerender within a Prerender? Is it something we
should re-evaluate on the WebKit side when the page becomes activated?

[cbentzel, 2011/03/14 14:32:26]

Ah, I see you are caching the values in the PrerenderManager to start the nested
prerenders when the page becomes activated. Let me look some more. 

[dominich, 2011/03/14 17:47:15]

This happens when we have a prerender link to a page with a prerender link.
WebKit could take this into account instead of doing it at the browser level,
but maybe in the future we'd want to do multiple prerenders and we might rate a
prerender from a prerendered page as higher priority than a second prerender on
the current page.

   prerender::PrerenderResourceHandler* pre_handler =
       prerender::PrerenderResourceHandler::MaybeCreate(*request,
                                                        context,
-                                                       handler);
+                                                       handler,
+                                                       is_from_prerender,
+                                                       route_id);

[cbentzel, 2011/03/14 14:32:26]

You need both child_id and route_id here. 

Not a huge deal now since we only allow 1 prerender at a time, but if this
loosens up it will break.

[dominich, 2011/03/14 17:47:15]

Done.

   if (pre_handler)
     handler = pre_handler;