**NOTFORLANDING** New link rel=prerender API

chrome/browser/prerender/prerender_link_manager.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_PRERENDER_PRERENDER_LINK_MANAGER_H_
+#define CHROME_BROWSER_PRERENDER_PRERENDER_LINK_MANAGER_H_
+#pragma once
+
+#include <map>
+#include <utility>
+
+#include "base/basictypes.h"
+#include "googleurl/src/gurl.h"
+
+class Profile;
+
+namespace content {
+class Referrer;
+}
+
+namespace gfx {
+class Size;
+}
+
+namespace prerender {
+
+class PrerenderManager;
+
+// Launch and cancel prerenders based on the LinkPrerender element events.
+class PrerenderLinkManager {

[cbentzel, 2012/03/29 00:13:37]

It's probably reasonable to unit test some of the management work this does. 

[gavinp, 2012/04/20 17:54:15]

Done.

+ public:
+  explicit PrerenderLinkManager(PrerenderManager* manager);
+  virtual ~PrerenderLinkManager();
+
+  static void OnNewLinkPrerender(
+      Profile* profile,
+      int prerender_id,
+      int child_id,
+      int render_view_route_id,
+      const GURL& url,
+      const content::Referrer& referrer,
+      const gfx::Size& size);
+  static void OnRemovedLinkPrerender(Profile* profile,

[cbentzel, 2012/03/29 00:13:37]

Document. What's different about OnRemoved versus OnUnloaded for example.

[gavinp, 2012/04/20 17:54:15]

The new names simplify this; it's Add, Cancel and Abandon.  Documented, too.

+                                     int prerender_id,
+                                     int child_id);
+  static void OnUnloadedLinkPrerender(Profile* profile,
+                                      int prerender_id,
+                                      int child_id);
+
+ private:
+  typedef std::pair<int, int> ChildAndPrerenderIdPair;
+  typedef std::map<ChildAndPrerenderIdPair, GURL> PrerenderIdToUrlMap;
+  typedef std::multimap<GURL, ChildAndPrerenderIdPair> UrlToPrerenderIdMap;

[mmenke, 2012/03/29 01:15:39]

Do we really need a multimap here?  Could just use a map with counts.  Seems a
little simpler to me, though, admittedly, removing things from it is marginally
more complicated.

[gavinp, 2012/04/20 17:54:15]

The problem with counts is that we're going to need the IDs shortly for sending
events down.  So while that fix works for this patch, that's no good even in the
near term.

So, about this map: it's with some measure of sorrow that I say it's actually
overly simple.  Treating GURL as the origin of this map ends up being broken. 
We need to key on more: the launching parameter of a prerender are the GURL, the
Referrer, and the session storage namespace.  If a launch matches those three,
it's the same.  Otherwise, it's not the same prerender.  The question is, what's
the complexity of having this logic in prerender_link_manager as well as
prerender_manager/prerender_tab_contents?  Some thought needs to go into getting
this right and not distributed across these three objects.

This upload though, I'm leaving it the same: child and GURL.  The result is that
I'll fail to launch some prerenders (same GURL, different referrer/namespace). 
To make the prerender_manager match properly on these is a lot of surgery that
feels separate from getting this messaging up here: and the brokenness is the
same as what we have already, anyway.

I'm thinking long and hard about how to capture this complexity without making
the upload implementing it awful.

+
+  void OnNewLinkPrerenderImpl(
+      int prerender_id,
+      int child_id,
+      int render_view_route_id,
+      const GURL& url,
+      const content::Referrer& referrer,
+      const gfx::Size& size);
+  void OnRemovedLinkPrerenderImpl(int prerender_id, int child_id);
+  void OnUnloadedLinkPrerenderImpl(int prerender_id, int child_id);
+
+  PrerenderManager* manager_;
+  PrerenderIdToUrlMap id_map_;
+  UrlToPrerenderIdMap url_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(PrerenderLinkManager);
+};
+
+}  // namespace prerender
+
+#endif  // CHROME_BROWSER_PRERENDER_PRERENDER_LINK_MANAGER_H_