Handle interface to prerenders.

chrome/browser/predictors/autocomplete_action_predictor.cc

 // 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.
 
 #include "chrome/browser/predictors/autocomplete_action_predictor.h"
 
 #include <math.h>
 
 #include <vector>
 
@@ skipping 133 matching lines @@
                   it->destination_url) == match_it->urls.end()) {
       match_it->urls.push_back(it->destination_url);
     }
   }
 }
 
 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(
         const string16& user_text,
         const AutocompleteMatch& match) const {
   bool is_in_db = false;
   const double confidence = CalculateConfidence(user_text, match, &is_in_db);
   DCHECK(confidence >= 0.0 && confidence <= 1.0);
 
   UMA_HISTOGRAM_BOOLEAN("AutocompleteActionPredictor.MatchIsInDb", is_in_db);
@@ skipping 136 matching lines @@
 
   const AutocompleteMatch& match = log.result.match_at(log.selected_index);
 
   UMA_HISTOGRAM_BOOLEAN(
       StringPrintf("Prerender.OmniboxNavigationsCouldPrerender%s",
                    prerender::PrerenderManager::GetModeString()).c_str(),
       prerender::IsOmniboxEnabled(profile_));
 
   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));
 
   // Traverse transitional matches for those that have a user_text that is a
   // prefix of |lower_user_text|.
   std::vector<AutocompleteActionPredictorTable::Row> rows_to_add;
   std::vector<AutocompleteActionPredictorTable::Row> rows_to_update;
 
   for (std::vector<TransitionalMatch>::const_iterator it =
         transitional_matches_.begin(); it != transitional_matches_.end();
@@ skipping 230 matching lines @@
   return number_of_hits / (number_of_hits + value.number_of_misses);
 }
 
 AutocompleteActionPredictor::TransitionalMatch::TransitionalMatch() {
 }
 
 AutocompleteActionPredictor::TransitionalMatch::~TransitionalMatch() {
 }
 
 }  // namespace predictors