Handle interface to prerenders.

chrome/browser/predictors/autocomplete_action_predictor.cc

Index: chrome/browser/predictors/autocomplete_action_predictor.cc
diff --git a/chrome/browser/predictors/autocomplete_action_predictor.cc b/chrome/browser/predictors/autocomplete_action_predictor.cc
index 33119069718a3581d6ee9b2de240c7176dd5f0fa..8804b985ff84bb54d6b2444e8398eae1df18501c 100644
--- a/chrome/browser/predictors/autocomplete_action_predictor.cc
+++ b/chrome/browser/predictors/autocomplete_action_predictor.cc
@@ -151,6 +151,19 @@ void AutocompleteActionPredictor::ClearTransitionalMatches() {
   transitional_matches_.clear();
 }
 
+prerender::PrerenderHandle AutocompleteActionPredictor::StartPrerendering(
+    const GURL& url,
+    content::SessionStorageNamespace* session_storage_namespace) {
+  if (prerender::PrerenderManager* prerender_manager =
+        prerender::PrerenderManagerFactory::GetForProfile(profile_)) {
+    prerender_ = prerender_manager->AddPrerenderFromOmnibox(
+        url, session_storage_namespace);
+    return prerender_;
+  }
+  prerender_ = prerender::PrerenderHandle();
+  return prerender_;
+}
+
 // Given a match, return a recommended action.
 AutocompleteActionPredictor::Action
     AutocompleteActionPredictor::RecommendAction(
@@ -307,14 +320,10 @@ void AutocompleteActionPredictor::OnOmniboxOpenedUrl(
 
   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 =
-      prerender::PrerenderManagerFactory::GetForProfile(profile_);
-  // |prerender_manager| can be NULL in incognito mode or if prerendering is
-  // otherwise disabled.
-  if (prerender_manager && !prerender_manager->IsPrerendering(opened_url))
-    prerender_manager->CancelOmniboxPrerenders();
+  // If the Omnibox triggered a prerender but the prerender doesn't match the
+  // one the user is navigating to, then we drop the prerender.
+  if (prerender_ != match.prerender)

[dominich, 2012/06/18 15:32:44]

This should not be pulled from the match. The prerender manager or handle should
be able to determine equivalence from the available information (URL/Session
Storage) that is already part of the match without adding this.

Please check with pkasting what he thinks about extending AutocompleteMatch this
way, but my gut is that it's not the right way to do it.

[gavinp, 2012/06/18 16:40:48]

We did talk about this at length, and I'm aware we differ here. PrerenderManager
shouldn't have a way to look through the list of running prerenders and get one
back besides "AddPrerender".  

Because omnibox prerendering is the only source here, we could just do away with
the weakptr on the match, and look only at prerender_, or even keep a list/set
of all launched prerenders (removing elements through an observer when they
destroy). I'll remove the element from the match in my next upload.

Or... have it both ways: should it call AddPrerender here?

+    prerender_ = prerender::PrerenderHandle();

[dominich, 2012/06/18 15:32:44]

if this has a side-effect of canceling a prerender then I don't like it at all.
It is completely non-obvious what this does, while an explicit call to
prerender_manager->CancelPrerender(prerender_) would be much clearer.

[gavinp, 2012/06/18 16:40:48]

And a runtime error if you try to drop a ref to a prerender that is running?

 
   const string16 lower_user_text(base::i18n::ToLower(log.text));