Cancel prerenders from Omnibox if we navigate to a different URL than predicted

chrome/browser/autocomplete/network_action_predictor.cc

Index: chrome/browser/autocomplete/network_action_predictor.cc
diff --git a/chrome/browser/autocomplete/network_action_predictor.cc b/chrome/browser/autocomplete/network_action_predictor.cc
index b43ee3c0167eaa6e4d10d2c8e22c1b400a202b08..12d9729e420da2ba7af6d614bc52c6a71bc49ccf 100644
--- a/chrome/browser/autocomplete/network_action_predictor.cc
+++ b/chrome/browser/autocomplete/network_action_predictor.cc
@@ -20,6 +20,8 @@
 #include "chrome/browser/history/history_notifications.h"
 #include "chrome/browser/history/in_memory_database.h"
 #include "chrome/browser/prerender/prerender_field_trial.h"
+#include "chrome/browser/prerender/prerender_manager.h"
+#include "chrome/browser/prerender/prerender_manager_factory.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/chrome_notification_types.h"
 #include "chrome/common/guid.h"
@@ -235,6 +237,13 @@ void NetworkActionPredictor::OnOmniboxOpenedUrl(const AutocompleteLog& log) {
 
   const GURL& opened_url = match.destination_url;
 
+  // If the Omnibox triggered a prerender but the URL doesn't match the one the
+  // user is navigating to, cancel the prerender.
+  prerender::PrerenderManager* prerender_manager =

[Peter Kasting, 2012/01/21 00:22:52]

Nit: Does it make sense to keep this as a member?  (It's not much different
either way, so I don't really have a preference.)

[dominich, 2012/01/23 22:50:07]

I prefer not to. It can't go away unexpectedly currently but that might change
so I prefer to keep these things loosely coupled.

+      prerender::PrerenderManagerFactory::GetForProfile(profile_);
+  if (prerender_manager && !prerender_manager->IsPrerendering(opened_url))

[Peter Kasting, 2012/01/21 00:22:52]

When is the manager NULL?  During testing?

(I try to limit NULL checks in our code to cases that truly need them.)

[cbentzel, 2012/01/21 02:29:09]

Right now we do NULL prerender_managers for incognito mode - this should change
soon, but isn't there yet.

[Peter Kasting, 2012/01/21 22:46:07]

Ah.  Perhaps this should get a "// |prerender_manager| may be NULL in incognito
mode." comment then?

[dominich, 2012/01/23 22:50:07]

Done.

+    prerender_manager->CancelOmniboxPrerenders();
+
   const string16 lower_user_text(base::i18n::ToLower(log.text));
 
   BeginTransaction();
@@ -291,7 +300,6 @@ void NetworkActionPredictor::OnOmniboxOpenedUrl(const AutocompleteLog& log) {
   tracked_urls_.clear();
 }
 
-
 void NetworkActionPredictor::DeleteOldIdsFromCaches(
     history::URLDatabase* url_db,
     std::vector<NetworkActionPredictorDatabase::Row::Id>* id_list) {