Handle interface to prerenders.

chrome/browser/prerender/prerender_manager.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/prerender/prerender_manager.h"
 
-#include <set>
+#include <algorithm>
+#include <functional>
 #include <string>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/logging.h"
 #include "base/memory/weak_ptr.h"
 #include "base/metrics/histogram.h"
 #include "base/stl_util.h"
 #include "base/time.h"
 #include "base/utf_string_conversions.h"
 #include "base/values.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/cancelable_request.h"
 #include "chrome/browser/favicon/favicon_tab_helper.h"
 #include "chrome/browser/prerender/prerender_condition.h"
 #include "chrome/browser/prerender/prerender_contents.h"
 #include "chrome/browser/prerender/prerender_field_trial.h"
 #include "chrome/browser/prerender/prerender_final_status.h"
+#include "chrome/browser/prerender/prerender_handle.h"
 #include "chrome/browser/prerender/prerender_histograms.h"
 #include "chrome/browser/prerender/prerender_history.h"
 #include "chrome/browser/prerender/prerender_local_predictor.h"
 #include "chrome/browser/prerender/prerender_manager_factory.h"
 #include "chrome/browser/prerender/prerender_tab_helper.h"
 #include "chrome/browser/prerender/prerender_tracker.h"
 #include "chrome/browser/prerender/prerender_util.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/tab_contents/core_tab_helper.h"
 #include "chrome/browser/ui/tab_contents/core_tab_helper_delegate.h"
@@ skipping 62 matching lines @@
 // This ensures that there is no bias in terms of the page load times
 // of the pages forming the difference between the two sets.
 
 bool NeedMatchCompleteDummyForFinalStatus(FinalStatus final_status) {
   return final_status != FINAL_STATUS_USED &&
       final_status != FINAL_STATUS_TIMED_OUT &&
       final_status != FINAL_STATUS_EVICTED &&
       final_status != FINAL_STATUS_MANAGER_SHUTDOWN &&
       final_status != FINAL_STATUS_APP_TERMINATING &&
       final_status != FINAL_STATUS_WINDOW_OPENER &&
-      final_status != FINAL_STATUS_FRAGMENT_MISMATCH &&
       final_status != FINAL_STATUS_CACHE_OR_HISTORY_CLEARED &&
       final_status != FINAL_STATUS_CANCELLED &&
-      final_status != FINAL_STATUS_SESSION_STORAGE_NAMESPACE_MISMATCH &&
       final_status != FINAL_STATUS_DEVTOOLS_ATTACHED &&
       final_status != FINAL_STATUS_CROSS_SITE_NAVIGATION_PENDING;
 }
 
 }  // namespace
 
 class PrerenderManager::OnCloseTabContentsDeleter
     : public content::WebContentsDelegate,
       public base::SupportsWeakPtr<
           PrerenderManager::OnCloseTabContentsDeleter> {
@@ skipping 41 matching lines @@
 // static
 bool PrerenderManager::is_prefetch_enabled_ = false;
 
 // static
 int PrerenderManager::prerenders_per_session_count_ = 0;
 
 // static
 PrerenderManager::PrerenderManagerMode PrerenderManager::mode_ =
     PRERENDER_MODE_ENABLED;
 
-struct PrerenderManager::PrerenderContentsData {
-  PrerenderContents* contents_;
-  base::Time start_time_;
-  int active_count_;
-  PrerenderContentsData(PrerenderContents* contents, base::Time start_time)
-      : contents_(contents),
-        start_time_(start_time),
-        active_count_(1) {
-    CHECK(contents);
-  }
-};
-
 struct PrerenderManager::NavigationRecord {
   GURL url_;
   base::TimeTicks time_;
   NavigationRecord(const GURL& url, base::TimeTicks time)
       : url_(url),
         time_(time) {
   }
 };
 
 PrerenderManager::PrerenderManager(Profile* profile,
@@ skipping 14 matching lines @@
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 }
 
 PrerenderManager::~PrerenderManager() {
 }
 
 void PrerenderManager::Shutdown() {
   DoShutdown();
 }
 
-bool PrerenderManager::AddPrerenderFromLinkRelPrerender(
+PrerenderHandle* PrerenderManager::AddPrerenderFromLinkRelPrerender(
     int process_id,
     int route_id,
     const GURL& url,
     const content::Referrer& referrer,
-    gfx::Size size) {
+    const gfx::Size& size) {
 #if defined(OS_ANDROID)
   // TODO(jcivelli): http://crbug.com/113322 We should have an option to disable
   //                link-prerender and enable omnibox-prerender only.
   return false;
 #else
-  std::pair<int, int> child_route_id_pair(process_id, route_id);
-  PrerenderContentsDataList::iterator it =
-      FindPrerenderContentsForChildRouteIdPair(child_route_id_pair);
-  if (it != prerender_list_.end()) {
+  DCHECK(!size.IsEmpty());
+  if (PrerenderData* parent_prerender_data =
+          FindPrerenderDataForChildAndRoute(process_id, route_id)) {
     // Instead of prerendering from inside of a running prerender, we will defer
     // this request until its launcher is made visible.
-    it->contents_->AddPendingPrerender(url, referrer, size);
-    return true;
+    if (PrerenderContents* contents = parent_prerender_data->contents_) {
+      pending_prerender_list_.push_back(
+          linked_ptr<PrerenderData>(new PrerenderData(this)));
+      PrerenderHandle* prerender_handle =
+          new PrerenderHandle(pending_prerender_list_.back().get());
+      contents->AddPendingPrerender(
+          prerender_handle->weak_ptr_factory_.GetWeakPtr(),
+          url, referrer, size);
+      return prerender_handle;
+    }
   }
 
   // Unit tests pass in a process_id == -1.
   SessionStorageNamespace* session_storage_namespace = NULL;
   if (process_id != -1) {
     RenderViewHost* source_render_view_host =
         RenderViewHost::FromID(process_id, route_id);
-    if (!source_render_view_host || !source_render_view_host->GetView())
-      return false;
+    if (!source_render_view_host)
+      return NULL;
     session_storage_namespace =
         source_render_view_host->GetSessionStorageNamespace();
-
-    if (size.IsEmpty()) {
-      // Use the size of the tab requesting the prerendering.
-      WebContents* web_contents =
-          WebContents::FromRenderViewHost(source_render_view_host);
-      if (web_contents && web_contents->GetView()) {
-        gfx::Rect container_bounds;
-        web_contents->GetView()->GetContainerBounds(&container_bounds);
-        size = container_bounds.size();
-      }
-    }
   }
 
   return AddPrerender(ORIGIN_LINK_REL_PRERENDER,
                       process_id, url, referrer, size,
                       session_storage_namespace);
 #endif
 }
 
-bool PrerenderManager::AddPrerenderFromOmnibox(
+PrerenderHandle* PrerenderManager::AddPrerenderFromOmnibox(
     const GURL& url,
     SessionStorageNamespace* session_storage_namespace,
-    gfx::Size size) {
+    const gfx::Size& size) {
   if (!IsOmniboxEnabled(profile_))
-    return false;
-  return AddPrerender(ORIGIN_OMNIBOX, -1, url,
-                      content::Referrer(), size,
+    return NULL;
+  return AddPrerender(ORIGIN_OMNIBOX, -1, url, content::Referrer(), size,
                       session_storage_namespace);
 }
 
-void PrerenderManager::MaybeCancelPrerender(const GURL& url) {
-  PrerenderContentsDataList::iterator it = FindPrerenderContentsForURL(url);
-  if (it == prerender_list_.end())
-    return;
-  PrerenderContentsData& prerender_contents_data = *it;
-  if (--prerender_contents_data.active_count_ == 0)
-    prerender_contents_data.contents_->Destroy(FINAL_STATUS_CANCELLED);
-}
-
 void PrerenderManager::DestroyPrerenderForRenderView(
     int process_id, int view_id, FinalStatus final_status) {
   DCHECK(CalledOnValidThread());
-  PrerenderContentsDataList::iterator it =
-      FindPrerenderContentsForChildRouteIdPair(
-          std::make_pair(process_id, view_id));
-  if (it != prerender_list_.end()) {
-    PrerenderContents* prerender_contents = it->contents_;
-    prerender_contents->Destroy(final_status);
+  if (PrerenderData* prerender_data =
+          FindPrerenderDataForChildAndRoute(process_id, view_id)) {
+    prerender_data->contents_->Destroy(final_status);
   }
 }
 
 void PrerenderManager::CancelAllPrerenders() {
   DCHECK(CalledOnValidThread());
-  while (!prerender_list_.empty()) {
-    PrerenderContentsData data = prerender_list_.front();
-    DCHECK(data.contents_);
-    data.contents_->Destroy(FINAL_STATUS_CANCELLED);
+  while (!active_prerender_list_.empty()) {
+    PrerenderContents* prerender_contents =
+        active_prerender_list_.front()->contents();
+    prerender_contents->Destroy(FINAL_STATUS_CANCELLED);
   }
 }
 
 bool PrerenderManager::MaybeUsePrerenderedPage(WebContents* web_contents,
                                                const GURL& url) {
   DCHECK(CalledOnValidThread());
   DCHECK(!IsWebContentsPrerendering(web_contents));
 
-  scoped_ptr<PrerenderContents> prerender_contents(
-      GetEntryButNotSpecifiedWC(url, web_contents));
-  if (prerender_contents.get() == NULL)
+  RenderViewHost* old_render_view_host = web_contents->GetRenderViewHost();
+
+  DeleteOldEntries();
+  DeletePendingDeleteEntries();
+  PrerenderData* prerender_data = FindPrerenderData(
+          url, old_render_view_host->GetSessionStorageNamespace());
+  if (!prerender_data)
     return false;
+  DCHECK(prerender_data->contents_);
+  if (IsNoSwapInExperiment(prerender_data->contents_->experiment_id()))
+    return false;
+
+  if (TabContents* new_tab_contents =
+      prerender_data->contents_->prerender_contents()) {
+    if (web_contents == new_tab_contents->web_contents())
+      return false;  // Do not swap in to ourself.
+  }
+
+  scoped_ptr<PrerenderContents> prerender_contents(prerender_data->contents_);
+  std::list<linked_ptr<PrerenderData> >::iterator to_erase =
+      FindIteratorForPrerenderContents(prerender_contents.get());
+  DCHECK(active_prerender_list_.end() != to_erase);
+  DCHECK_EQ(prerender_data, to_erase->get());
+  active_prerender_list_.erase(to_erase);
 
   // Do not use the prerendered version if there is an opener object.
   if (web_contents->HasOpener()) {
     prerender_contents.release()->Destroy(FINAL_STATUS_WINDOW_OPENER);
     return false;
   }
 
-  // Even if we match, the location.hash might be different. Record this as a
-  // separate final status.
-  GURL matching_url;
-  bool url_matches = prerender_contents->MatchesURL(url, &matching_url);
-  DCHECK(url_matches);
-  if (url_matches && url.ref() != matching_url.ref()) {
-    prerender_contents.release()->Destroy(FINAL_STATUS_FRAGMENT_MISMATCH);
-    return false;
-  }
-
   // If we are just in the control group (which can be detected by noticing
   // that prerendering hasn't even started yet), record that |web_contents| now
   // would be showing a prerendered contents, but otherwise, don't do anything.
   if (!prerender_contents->prerendering_has_started()) {
     MarkWebContentsAsWouldBePrerendered(web_contents);
     prerender_contents.release()->Destroy(FINAL_STATUS_WOULD_HAVE_BEEN_USED);
     return false;
   }
 
   // Don't use prerendered pages if debugger is attached to the tab.
   // See http://crbug.com/98541
   if (content::DevToolsAgentHostRegistry::IsDebuggerAttached(web_contents)) {
     DestroyAndMarkMatchCompleteAsUsed(prerender_contents.release(),
                                       FINAL_STATUS_DEVTOOLS_ATTACHED);
     return false;
   }
 
   // If the prerendered page is in the middle of a cross-site navigation,
   // don't swap it in because there isn't a good way to merge histories.
   if (prerender_contents->IsCrossSiteNavigationPending()) {
     DestroyAndMarkMatchCompleteAsUsed(
         prerender_contents.release(),
         FINAL_STATUS_CROSS_SITE_NAVIGATION_PENDING);
     return false;
   }
 
-  // If the session storage namespaces don't match, cancel the prerender.
-  RenderViewHost* old_render_view_host = web_contents->GetRenderViewHost();
-  RenderViewHost* new_render_view_host =
-      prerender_contents->prerender_contents()->web_contents()->
-          GetRenderViewHost();
-  DCHECK(old_render_view_host);
-  DCHECK(new_render_view_host);
-  if (old_render_view_host->GetSessionStorageNamespace() !=
-      new_render_view_host->GetSessionStorageNamespace()) {
-    DestroyAndMarkMatchCompleteAsUsed(
-        prerender_contents.release(),
-        FINAL_STATUS_SESSION_STORAGE_NAMESPACE_MISMATCH);
-    return false;
-  }
-
-  // If we don't want to use prerenders at all, we are done.
   // For bookkeeping purposes, we need to mark this WebContents to
   // reflect that it would have been prerendered.
   if (GetMode() == PRERENDER_MODE_EXPERIMENT_NO_USE_GROUP) {
     MarkWebContentsAsWouldBePrerendered(web_contents);
     prerender_contents.release()->Destroy(FINAL_STATUS_WOULD_HAVE_BEEN_USED);
     return false;
   }
 
   int child_id, route_id;
   CHECK(prerender_contents->GetChildId(&child_id));
   CHECK(prerender_contents->GetRouteId(&route_id));
 
   // Try to set the prerendered page as used, so any subsequent attempts to
   // cancel on other threads will fail.  If this fails because the prerender
   // was already cancelled, possibly on another thread, fail.
   if (!prerender_tracker_->TryUse(child_id, route_id))
     return false;
 
+  // At this point, we've determined that we will use the prerender.
+
   if (!prerender_contents->load_start_time().is_null()) {
     histograms_->RecordTimeUntilUsed(GetCurrentTimeTicks() -
                                      prerender_contents->load_start_time(),
                                      GetMaxAge());
   }
 
   histograms_->RecordPerSessionCount(++prerenders_per_session_count_);
   histograms_->RecordUsedPrerender(prerender_contents->origin());
   prerender_contents->set_final_status(FINAL_STATUS_USED);
 
+  RenderViewHost* new_render_view_host =
+      prerender_contents->prerender_contents()->web_contents()->
+          GetRenderViewHost();
   new_render_view_host->Send(
       new PrerenderMsg_SetIsPrerendering(new_render_view_host->GetRoutingID(),
                                          false));
 
+  // Start pending prerender requests from the PrerenderContents, if there are
+  // any.
+  prerender_contents->StartPendingPrerenders();
+
   TabContents* new_tab_contents =
       prerender_contents->ReleasePrerenderContents();
   TabContents* old_tab_contents = TabContents::FromWebContents(web_contents);
   DCHECK(new_tab_contents);
   DCHECK(old_tab_contents);
 
   MarkWebContentsAsPrerendered(new_tab_contents->web_contents());
 
   // Merge the browsing history.
   new_tab_contents->web_contents()->GetController().CopyStateFromAndPrune(
@@ skipping 12 matching lines @@
   }
 
   // Update PPLT metrics:
   // If the tab has finished loading, record a PPLT of 0.
   // If the tab is still loading, reset its start time to the current time.
   PrerenderTabHelper* prerender_tab_helper =
       new_tab_contents->prerender_tab_helper();
   DCHECK(prerender_tab_helper != NULL);
   prerender_tab_helper->PrerenderSwappedIn();
 
-  // Start pending prerender requests from the PrerenderContents, if there are
-  // any.
-  prerender_contents->StartPendingPrerenders();
-
   if (old_tab_contents->web_contents()->NeedToFireBeforeUnload()) {
     // Schedule the delete to occur after the tab has run its unload handlers.
     on_close_tab_contents_deleters_.push_back(
         new OnCloseTabContentsDeleter(this, old_tab_contents));
     old_tab_contents->web_contents()->GetRenderViewHost()->
         FirePageBeforeUnload(false);
   } else {
     // No unload handler to run, so delete asap.
     ScheduleDeleteOldTabContents(old_tab_contents, NULL);
   }
 
   // TODO(cbentzel): Should prerender_contents move to the pending delete
   //                 list, instead of deleting directly here?
   AddToHistory(prerender_contents.get());
   RecordNavigation(url);
   return true;
 }
 
 void PrerenderManager::MoveEntryToPendingDelete(PrerenderContents* entry,
                                                 FinalStatus final_status) {
   DCHECK(CalledOnValidThread());
   DCHECK(entry);
   // Confirm this entry has not already been moved to the pending delete list.
   DCHECK_EQ(0, std::count(pending_delete_list_.begin(),
                           pending_delete_list_.end(), entry));
 
-  for (PrerenderContentsDataList::iterator it = prerender_list_.begin();
-       it != prerender_list_.end();
-       ++it) {
-    if (it->contents_ == entry) {
-      bool swapped_in_dummy_replacement = false;
+  std::list<linked_ptr<PrerenderData> >::iterator it =
+      FindIteratorForPrerenderContents(entry);
 
-      // If this PrerenderContents is being deleted due to a cancellation,
-      // we need to create a dummy replacement for PPLT accounting purposes
-      // for the Match Complete group.
-      // This is the case if the cancellation is for any reason that would not
-      // occur in the control group case.
-      if (entry->match_complete_status() ==
-          PrerenderContents::MATCH_COMPLETE_DEFAULT &&
-          NeedMatchCompleteDummyForFinalStatus(final_status) &&
-          ActuallyPrerendering()) {
-        // TODO(tburkard): I'd like to DCHECK that we are actually prerendering.
-        // However, what if new conditions are added and
-        // NeedMatchCompleteDummyForFinalStatus, is not being updated.  Not sure
-        // what's the best thing to do here.  For now, I will just check whether
-        // we are actually prerendering.
-        entry->set_match_complete_status(
-            PrerenderContents::MATCH_COMPLETE_REPLACED);
-        if (PrerenderContents* dummy_replacement_prerender_contents =
-                CreatePrerenderContents(entry->prerender_url(),
-                                        entry->referrer(),
-                                        entry->origin(),
-                                        entry->experiment_id())) {
-          dummy_replacement_prerender_contents->set_match_complete_status(
-              PrerenderContents::MATCH_COMPLETE_REPLACEMENT_PENDING);
-          if (!dummy_replacement_prerender_contents->Init())
-            break;
-          dummy_replacement_prerender_contents->
-              AddAliasURLsFromOtherPrerenderContents(entry);
-          dummy_replacement_prerender_contents->set_match_complete_status(
-              PrerenderContents::MATCH_COMPLETE_REPLACEMENT);
-          it->contents_ = dummy_replacement_prerender_contents;
-          swapped_in_dummy_replacement = true;
-        }
-      }
-      if (!swapped_in_dummy_replacement)
-        prerender_list_.erase(it);
-      break;
+  // If this PrerenderContents is being deleted due to a cancellation,
+  // we need to create a dummy replacement for PPLT accounting purposes
+  // for the Match Complete group.
+  // This is the case if the cancellation is for any reason that would not
+  // occur in the control group case.
+  if (it != active_prerender_list_.end()) {
+    if (entry->match_complete_status() ==
+            PrerenderContents::MATCH_COMPLETE_DEFAULT &&
+        NeedMatchCompleteDummyForFinalStatus(final_status) &&
+        ActuallyPrerendering()) {
+      // TODO(tburkard): I'd like to DCHECK that we are actually prerendering.
+      // However, what if new conditions are added and
+      // NeedMatchCompleteDummyForFinalStatus, is not being updated.  Not sure
+      // what's the best thing to do here.  For now, I will just check whether
+      // we are actually prerendering.
+      entry->set_match_complete_status(
+          PrerenderContents::MATCH_COMPLETE_REPLACED);
+      PrerenderContents* dummy_replacement_prerender_contents =
+          CreatePrerenderContents(entry->prerender_url(), entry->referrer(),
+                                  entry->origin(), entry->experiment_id());
+      dummy_replacement_prerender_contents->MakeIntoDummyReplacementOf(entry);
+      DCHECK(dummy_replacement_prerender_contents);
+
+      dummy_replacement_prerender_contents->set_match_complete_status(
+          PrerenderContents::MATCH_COMPLETE_REPLACEMENT_PENDING);
+      DCHECK(dummy_replacement_prerender_contents->Init());
+      dummy_replacement_prerender_contents->
+          AddAliasURLsFromOtherPrerenderContents(entry);
+      dummy_replacement_prerender_contents->set_match_complete_status(
+          PrerenderContents::MATCH_COMPLETE_REPLACEMENT);
+
+      it->get()->contents_ = dummy_replacement_prerender_contents;
+    } else {
+      active_prerender_list_.erase(it);
     }
   }
+
   AddToHistory(entry);
   pending_delete_list_.push_back(entry);
 
   // Destroy the old WebContents relatively promptly to reduce resource usage,
   // and in the case of HTML5 media, reduce the change of playing any sound.
   PostCleanupTask();
 }
 
 // static
 void PrerenderManager::RecordPerceivedPageLoadTime(
@@ skipping 90 matching lines @@
 }
 
 // static
 bool PrerenderManager::IsNoUseGroup() {
   return GetMode() == PRERENDER_MODE_EXPERIMENT_NO_USE_GROUP;
 }
 
 bool PrerenderManager::IsWebContentsPrerendering(
     WebContents* web_contents) const {
   DCHECK(CalledOnValidThread());
-  for (PrerenderContentsDataList::const_iterator it = prerender_list_.begin();
-       it != prerender_list_.end();
+  for (std::list<linked_ptr<PrerenderData> >::const_iterator it =
+           active_prerender_list_.begin();
+       it != active_prerender_list_.end();
        ++it) {
-    TabContents* prerender_tab_contents = it->contents_->prerender_contents();
+    TabContents* prerender_tab_contents =
+        it->get()->contents_->prerender_contents();
     if (prerender_tab_contents &&
         prerender_tab_contents->web_contents() == web_contents) {
       return true;
     }
   }
 
   // Also look through the pending-deletion list.
   for (std::list<PrerenderContents*>::const_iterator it =
            pending_delete_list_.begin();
        it != pending_delete_list_.end();
        ++it) {
     TabContents* prerender_tab_contents = (*it)->prerender_contents();
     if (prerender_tab_contents &&
         prerender_tab_contents->web_contents() == web_contents)
       return true;
   }
 
   return false;
 }
 
-bool PrerenderManager::DidPrerenderFinishLoading(const GURL& url) const {
-  DCHECK(CalledOnValidThread());
-  PrerenderContents* contents = FindEntry(url);
-  return contents ? contents->has_finished_loading() : false;
-}
-
 void PrerenderManager::MarkWebContentsAsPrerendered(WebContents* web_contents) {
   DCHECK(CalledOnValidThread());
   prerendered_tab_contents_set_.insert(web_contents);
 }
 
 void PrerenderManager::MarkWebContentsAsWouldBePrerendered(
     WebContents* web_contents) {
   DCHECK(CalledOnValidThread());
   would_be_prerendered_map_[web_contents] = true;
 }
@@ skipping 95 matching lines @@
   histograms_->RecordFinalStatus(origin,
                                  experiment_id,
                                  mc_status,
                                  final_status);
 }
 
 void PrerenderManager::AddCondition(const PrerenderCondition* condition) {
   prerender_conditions_.push_back(condition);
 }
 
-bool PrerenderManager::IsPendingEntry(const GURL& url) const {
-  DCHECK(CalledOnValidThread());
-  for (PrerenderContentsDataList::const_iterator it = prerender_list_.begin();
-       it != prerender_list_.end();
-       ++it) {
-    if (it->contents_->IsPendingEntry(url))
-      return true;
-  }
-  return false;
-}
-
-bool PrerenderManager::IsPrerendering(const GURL& url) const {
-  DCHECK(CalledOnValidThread());
-  return (FindEntry(url) != NULL);
-}
-
 void PrerenderManager::RecordNavigation(const GURL& url) {
   DCHECK(CalledOnValidThread());
 
   navigations_.push_back(NavigationRecord(url, GetCurrentTimeTicks()));
   CleanUpOldNavigations();
 }
 
 // protected
+PrerenderManager::PrerenderData::PrerenderData(PrerenderManager* manager)
+    : manager_(manager), contents_(NULL), handle_count_(0) {
+}
+
+PrerenderManager::PrerenderData::PrerenderData(PrerenderManager* manager,
+                                               PrerenderContents* contents)
+    : manager_(manager), contents_(contents), handle_count_(0) {
+}
+
+void PrerenderManager::PrerenderData::OnNewHandle() {
+  DCHECK(contents_ || handle_count_ == 0) <<
+      "Cannot create multiple handles to a pending prerender.";
+  ++handle_count_;
+}
+
+void PrerenderManager::PrerenderData::OnNavigateAwayByHandle() {
+  // TODO(gavinp): Implement reasonable behaviour for navigation away from
+  // launcher. We can't just call OnCancel, because many cases have redirect
+  // chains that will eventually lead to the correct prerendered page, and we
+  // don't want to delete our prerender just as it is going to be used.
+
+  if (!contents_) {
+    DCHECK_EQ(1, handle_count_);
+    // Pending prerenders are not maintained in the active_prerender_list_, so
+    // they will not get normal expiry. Since this prerender hasn't even been
+    // launched yet, and it's held by a page that is being prerendered, we will
+    // just delete it.
+    manager_->DestroyPendingPrerenderData(this);
+  }
+}
+
+void PrerenderManager::PrerenderData::OnCancelByHandle() {
+  DCHECK_LE(1, handle_count_);
+  DCHECK(contents_ || handle_count_ == 1);
+
+  if (--handle_count_ == 0) {
+    if (contents_) {
+      // This will eventually remove this object from active_prerender_list_,
+      // triggering the linked_ptr auto deletion.
+      contents_->Destroy(FINAL_STATUS_CANCELLED);
+    } else {
+      manager_->DestroyPendingPrerenderData(this);
+    }
+  }
+}
+
+PrerenderManager::PrerenderData::~PrerenderData() {
+}
+
 void PrerenderManager::SetPrerenderContentsFactory(
     PrerenderContents::Factory* prerender_contents_factory) {
   DCHECK(CalledOnValidThread());
   prerender_contents_factory_.reset(prerender_contents_factory);
 }
 
+void PrerenderManager::StartPendingPrerender(
+    PrerenderHandle* existing_prerender_handle,
+    Origin origin,
+    int process_id,
+    const GURL& url,
+    const content::Referrer& referrer,
+    const gfx::Size& size,
+    content::SessionStorageNamespace* session_storage_namespace) {
+  DCHECK(existing_prerender_handle);
+  DCHECK(existing_prerender_handle->IsValid());
+  DCHECK(existing_prerender_handle->IsPending());
+
+  DVLOG(6) << "StartPendingPrerender";
+  DVLOG(6) << "existing_prerender_handle->handle_count_ = " <<
+      existing_prerender_handle->prerender_data_->handle_count_;
+
+  DCHECK(process_id == -1 || session_storage_namespace);
+
+  scoped_ptr<PrerenderHandle> swap_prerender_handle(AddPrerender(
+      origin, process_id, url, referrer, size, session_storage_namespace));
+  if (swap_prerender_handle.get()) {
+    // AddPrerender has returned a new prerender handle to us. We want to make
+    // |existing_prerender_handle| active, so swap the underlying PrerenderData
+    // between the two handles, and delete our old handle (which will release
+    // our entry in the pending_prerender_list_).
+    existing_prerender_handle->SwapPrerenderDataWith(
+        swap_prerender_handle.get());
+    swap_prerender_handle->OnCancel();
+    return;
+  }
+
+  // We could not start our Prerender. Canceling the existing handle will make
+  // it return false for PrerenderHandle::IsPending(), and will release the
+  // PrerenderData from pending_prerender_list_.
+  existing_prerender_handle->OnCancel();
+}
+
+void PrerenderManager::DestroyPendingPrerenderData(
+    PrerenderData* pending_prerender_data) {
+  for (std::list<linked_ptr<PrerenderData> >::iterator
+           it = pending_prerender_list_.begin();
+       it != pending_prerender_list_.end();
+       ++it) {
+    if (it->get() == pending_prerender_data) {
+      DCHECK_GE(1, it->get()->handle_count_);
+      pending_prerender_list_.erase(it);
+      return;
+    }
+  }
+  NOTREACHED();
+}
+
 void PrerenderManager::DoShutdown() {
   DestroyAllContents(FINAL_STATUS_MANAGER_SHUTDOWN);
   STLDeleteElements(&prerender_conditions_);
   on_close_tab_contents_deleters_.reset();
   profile_ = NULL;
+
+  DCHECK(active_prerender_list_.empty());
 }
 
 // private
-bool PrerenderManager::AddPrerender(
+PrerenderHandle* PrerenderManager::AddPrerender(
     Origin origin,
     int process_id,
     const GURL& url_arg,
     const content::Referrer& referrer,
-    gfx::Size size,
+    const gfx::Size& size,
     SessionStorageNamespace* session_storage_namespace) {
   DCHECK(CalledOnValidThread());
 
   if (!IsEnabled())
-    return false;
+    return NULL;
 
   if (origin == ORIGIN_LINK_REL_PRERENDER &&
       IsGoogleSearchResultURL(referrer.url)) {
     origin = ORIGIN_GWS_PRERENDER;
   }
 
   DeleteOldEntries();
   DeletePendingDeleteEntries();
 
   GURL url = url_arg;
   GURL alias_url;
   uint8 experiment = GetQueryStringBasedExperiment(url_arg);
   bool control_group_behavior =
       IsControlGroup() || IsControlGroupExperiment(experiment);
   if (control_group_behavior &&
       MaybeGetQueryStringBasedAliasURL(url, &alias_url)) {
     url = alias_url;
   }
 
   // From here on, we will record a FinalStatus so we need to register with the
   // histogram tracking.
   histograms_->RecordPrerender(origin, url_arg);
 
-  if (PrerenderContentsData* prerender_contents_data = FindEntryData(url)) {
-    ++prerender_contents_data->active_count_;
+  if (PrerenderData* preexisting_prerender_data =
+          FindPrerenderData(url, session_storage_namespace)) {
     RecordFinalStatus(origin, experiment, FINAL_STATUS_DUPLICATE);
-    return true;
+    return new PrerenderHandle(preexisting_prerender_data);
   }
 
   // Do not prerender if there are too many render processes, and we would
   // have to use an existing one.  We do not want prerendering to happen in
   // a shared process, so that we can always reliably lower the CPU
   // priority for prerendering.
   // In single-process mode, ShouldTryToUseExistingProcessHost() always returns
   // true, so that case needs to be explicitly checked for.
   // TODO(tburkard): Figure out how to cancel prerendering in the opposite
   // case, when a new tab is added to a process used for prerendering.
   // On Android we do reuse processes as we have a limited number of them and we
   // still want the benefits of prerendering even when several tabs are open.
 #if !defined(OS_ANDROID)
   if (content::RenderProcessHost::ShouldTryToUseExistingProcessHost(
           profile_, url) &&
       !content::RenderProcessHost::run_renderer_in_process()) {
     RecordFinalStatus(origin, experiment, FINAL_STATUS_TOO_MANY_PROCESSES);
-    return false;
+    return NULL;
   }
 #endif
 
   // Check if enough time has passed since the last prerender.
   if (!DoesRateLimitAllowPrerender()) {
     // Cancel the prerender. We could add it to the pending prerender list but
     // this doesn't make sense as the next prerender request will be triggered
     // by a navigation and is unlikely to be the same site.
     RecordFinalStatus(origin, experiment, FINAL_STATUS_RATE_LIMIT_EXCEEDED);
-    return false;
+    return NULL;
   }
 
   PrerenderContents* prerender_contents = CreatePrerenderContents(
       url, referrer, origin, experiment);
   if (!prerender_contents || !prerender_contents->Init())
-    return false;
+    return NULL;
 
   histograms_->RecordPrerenderStarted(origin);
 
   // TODO(cbentzel): Move invalid checks here instead of PrerenderContents?
-  PrerenderContentsData data(prerender_contents, GetCurrentTime());
-
-  prerender_list_.push_back(data);
+  active_prerender_list_.push_back(
+      linked_ptr<PrerenderData>(new PrerenderData(this, prerender_contents)));
+  PrerenderHandle* prerender_handle =
+      new PrerenderHandle(active_prerender_list_.back().get());
 
   last_prerender_start_time_ = GetCurrentTimeTicks();
 
-  if (size.IsEmpty())
-    size = config_.default_tab_bounds.size();
+  gfx::Size contents_size =
+      size.IsEmpty() ? config_.default_tab_bounds.size() : size;
 
-  data.contents_->StartPrerendering(process_id, size, session_storage_namespace,
-                                    control_group_behavior);
+  prerender_contents->StartPrerendering(process_id, contents_size,
+                                        session_storage_namespace,
+                                        control_group_behavior);
 
-  while (prerender_list_.size() > config_.max_elements) {
-    data = prerender_list_.front();
-    prerender_list_.pop_front();
-    data.contents_->Destroy(FINAL_STATUS_EVICTED);
+  while (active_prerender_list_.size() > config_.max_elements) {
+    prerender_contents = active_prerender_list_.front()->contents_;
+    DCHECK(prerender_contents);
+    prerender_contents->Destroy(FINAL_STATUS_EVICTED);
   }
+
   StartSchedulingPeriodicCleanups();
-  return true;
-}
-
-PrerenderContents* PrerenderManager::GetEntry(const GURL& url) {
-  return GetEntryButNotSpecifiedWC(url, NULL);
-}
-
-PrerenderContents* PrerenderManager::GetEntryButNotSpecifiedWC(
-    const GURL& url,
-    WebContents* wc) {
-  DCHECK(CalledOnValidThread());
-  DeleteOldEntries();
-  DeletePendingDeleteEntries();
-  for (PrerenderContentsDataList::iterator it = prerender_list_.begin();
-       it != prerender_list_.end();
-       ++it) {
-    PrerenderContents* prerender_contents = it->contents_;
-    if (prerender_contents->MatchesURL(url, NULL) &&
-        !IsNoSwapInExperiment(prerender_contents->experiment_id())) {
-      if (!prerender_contents->prerender_contents() ||
-          !wc ||
-          prerender_contents->prerender_contents()->web_contents() != wc) {
-        prerender_list_.erase(it);
-        return prerender_contents;
-      }
-    }
-  }
-  // Entry not found.
-  return NULL;
+  return prerender_handle;
 }
 
 void PrerenderManager::StartSchedulingPeriodicCleanups() {
   DCHECK(CalledOnValidThread());
   if (repeating_timer_.IsRunning())
     return;
   repeating_timer_.Start(FROM_HERE,
       base::TimeDelta::FromMilliseconds(kPeriodicCleanupIntervalMs),
       this,
       &PrerenderManager::PeriodicCleanup);
 }
 
-void PrerenderManager::MaybeStopSchedulingPeriodicCleanups() {
-  if (!prerender_list_.empty())
-    return;
-
+void PrerenderManager::StopSchedulingPeriodicCleanups() {
   DCHECK(CalledOnValidThread());
   repeating_timer_.Stop();
 }
 
 void PrerenderManager::PeriodicCleanup() {
   DCHECK(CalledOnValidThread());
   DeleteOldTabContents();
   DeleteOldEntries();
+  if (active_prerender_list_.empty())
+    StopSchedulingPeriodicCleanups();
 
   // Grab a copy of the current PrerenderContents pointers, so that we
   // will not interfere with potential deletions of the list.
   std::vector<PrerenderContents*> prerender_contents;
-  for (PrerenderContentsDataList::iterator it = prerender_list_.begin();
-       it != prerender_list_.end();
-       ++it) {
-    DCHECK(it->contents_);
-    prerender_contents.push_back(it->contents_);
+  prerender_contents.reserve(active_prerender_list_.size());
+  for (std::list<linked_ptr<PrerenderData> >::iterator
+           it = active_prerender_list_.begin();
+      it != active_prerender_list_.end();
+      ++it) {
+    prerender_contents.push_back(it->get()->contents_);
   }
-  for (std::vector<PrerenderContents*>::iterator it =
-           prerender_contents.begin();
-       it != prerender_contents.end();
-       ++it) {
-    (*it)->DestroyWhenUsingTooManyResources();
-  }
+  std::for_each(prerender_contents.begin(), prerender_contents.end(),
+                std::mem_fun(
+                    &PrerenderContents::DestroyWhenUsingTooManyResources));
 
   DeletePendingDeleteEntries();
 }
 
 void PrerenderManager::PostCleanupTask() {
   DCHECK(CalledOnValidThread());
   MessageLoop::current()->PostTask(
       FROM_HERE,
       base::Bind(&PrerenderManager::PeriodicCleanup,
                  weak_factory_.GetWeakPtr()));
 }
 
 base::TimeDelta PrerenderManager::GetMaxAge() const {
   return (GetMode() == PRERENDER_MODE_EXPERIMENT_5MIN_TTL_GROUP ?
       base::TimeDelta::FromSeconds(300) : config_.max_age);
 }
 
-bool PrerenderManager::IsPrerenderElementFresh(const base::Time start) const {
+bool PrerenderManager::IsPrerenderFresh(const base::TimeTicks start) const {
   DCHECK(CalledOnValidThread());
-  base::Time now = GetCurrentTime();
-  return (now - start < GetMaxAge());
+  return GetCurrentTimeTicks() - start < GetMaxAge();
 }
 
 void PrerenderManager::DeleteOldEntries() {
   DCHECK(CalledOnValidThread());
-  while (!prerender_list_.empty()) {
-    PrerenderContentsData data = prerender_list_.front();
-    if (IsPrerenderElementFresh(data.start_time_))
+  while (!active_prerender_list_.empty()) {
+    PrerenderContents* contents = active_prerender_list_.front()->contents_;
+    DCHECK(contents);
+    if (IsPrerenderFresh(contents->load_start_time()))
       return;
-    data.contents_->Destroy(FINAL_STATUS_TIMED_OUT);
+    contents->Destroy(FINAL_STATUS_TIMED_OUT);
   }
-  MaybeStopSchedulingPeriodicCleanups();
 }
 
 base::Time PrerenderManager::GetCurrentTime() const {
   return base::Time::Now();
 }
 
 base::TimeTicks PrerenderManager::GetCurrentTimeTicks() const {
   return base::TimeTicks::Now();
 }
 
 PrerenderContents* PrerenderManager::CreatePrerenderContents(
     const GURL& url,
     const content::Referrer& referrer,
     Origin origin,
     uint8 experiment_id) {
   DCHECK(CalledOnValidThread());
   return prerender_contents_factory_->CreatePrerenderContents(
       this, prerender_tracker_, profile_, url,
       referrer, origin, experiment_id);
 }
 
 void PrerenderManager::DeletePendingDeleteEntries() {
   while (!pending_delete_list_.empty()) {
     PrerenderContents* contents = pending_delete_list_.front();
     pending_delete_list_.pop_front();
     delete contents;
   }
 }
 
-PrerenderManager::PrerenderContentsData* PrerenderManager::FindEntryData(
-    const GURL& url) {
-  DCHECK(CalledOnValidThread());
-  PrerenderContentsDataList::iterator it = FindPrerenderContentsForURL(url);
-  if (it == prerender_list_.end())
-    return NULL;
-  PrerenderContentsData& prerender_contents_data = *it;
-  return &prerender_contents_data;
-}
-
-PrerenderContents* PrerenderManager::FindEntry(const GURL& url) const {
-  DCHECK(CalledOnValidThread());
-  for (PrerenderContentsDataList::const_iterator it = prerender_list_.begin();
-       it != prerender_list_.end();
+PrerenderManager::PrerenderData* PrerenderManager::FindPrerenderData(
+    const GURL& url,
+    const SessionStorageNamespace* session_storage_namespace) {
+  for (std::list<linked_ptr<PrerenderData> >::iterator
+           it = active_prerender_list_.begin();
+       it != active_prerender_list_.end();
        ++it) {
-    if (it->contents_->MatchesURL(url, NULL))
-      return it->contents_;
+    PrerenderContents* prerender_contents = it->get()->contents_;
+    if (prerender_contents->Matches(url, session_storage_namespace))
+      return it->get();
   }
-  // Entry not found.
   return NULL;
 }
 
-PrerenderManager::PrerenderContentsDataList::iterator
-    PrerenderManager::FindPrerenderContentsForChildRouteIdPair(
-        const std::pair<int, int>& child_route_id_pair) {
-  PrerenderContentsDataList::iterator it = prerender_list_.begin();
-  for (; it != prerender_list_.end(); ++it) {
-    PrerenderContents* prerender_contents = it->contents_;
+PrerenderManager::PrerenderData*
+PrerenderManager::FindPrerenderDataForChildAndRoute(
+    const int child_id, const int route_id) {
+  for (std::list<linked_ptr<PrerenderData> >::iterator
+           it = active_prerender_list_.begin();
+       it != active_prerender_list_.end();
+       ++it) {
+    PrerenderContents* prerender_contents = it->get()->contents_;
 
-    int child_id;
-    int route_id;
-    bool has_child_id = prerender_contents->GetChildId(&child_id);
-    bool has_route_id = has_child_id &&
-                        prerender_contents->GetRouteId(&route_id);
+    int contents_child_id;
+    if (!prerender_contents->GetChildId(&contents_child_id))
+      continue;
+    int contents_route_id;
+    if (!prerender_contents->GetRouteId(&contents_route_id))
+      continue;
 
-    if (has_child_id && has_route_id &&
-        child_id == child_route_id_pair.first &&
-        route_id == child_route_id_pair.second) {
-      break;
-    }
+    if (contents_child_id == child_id && contents_route_id == route_id)
+      return it->get();
   }
-  return it;
+  return NULL;
 }
 
-PrerenderManager::PrerenderContentsDataList::iterator
-    PrerenderManager::FindPrerenderContentsForURL(const GURL& url) {
-  for (PrerenderContentsDataList::iterator it = prerender_list_.begin();
-       it != prerender_list_.end(); ++it) {
-    if (it->contents_->MatchesURL(url, NULL))
+std::list<linked_ptr<PrerenderManager::PrerenderData> >::iterator
+PrerenderManager::FindIteratorForPrerenderContents(
+    PrerenderContents* prerender_contents) {
+  for (std::list<linked_ptr<PrerenderData> >::iterator
+           it = active_prerender_list_.begin();
+       it != active_prerender_list_.end();
+       ++it) {
+    if (prerender_contents == it->get()->contents_)
       return it;
   }
-  return prerender_list_.end();
+  return active_prerender_list_.end();
 }
 
 bool PrerenderManager::DoesRateLimitAllowPrerender() const {
   DCHECK(CalledOnValidThread());
   base::TimeDelta elapsed_time =
       GetCurrentTimeTicks() - last_prerender_start_time_;
   histograms_->RecordTimeBetweenPrerenderRequests(elapsed_time);
   if (!config_.rate_limit_enabled)
     return true;
   return elapsed_time >
@@ skipping 41 matching lines @@
 void PrerenderManager::AddToHistory(PrerenderContents* contents) {
   PrerenderHistory::Entry entry(contents->prerender_url(),
                                 contents->final_status(),
                                 contents->origin(),
                                 base::Time::Now());
   prerender_history_->AddEntry(entry);
 }
 
 Value* PrerenderManager::GetActivePrerendersAsValue() const {
   ListValue* list_value = new ListValue();
-  for (PrerenderContentsDataList::const_iterator it = prerender_list_.begin();
-       it != prerender_list_.end();
+  for (std::list<linked_ptr<PrerenderData> >::const_iterator it =
+           active_prerender_list_.begin();
+       it != active_prerender_list_.end();
        ++it) {
-    Value* prerender_value = it->contents_->GetAsValue();
-    if (!prerender_value)
-      continue;
-    list_value->Append(prerender_value);
+    if (Value* prerender_value = it->get()->contents_->GetAsValue())
+      list_value->Append(prerender_value);
   }
   return list_value;
 }
 
 void PrerenderManager::DestroyAllContents(FinalStatus final_status) {
   DeleteOldTabContents();
-  while (!prerender_list_.empty()) {
-    PrerenderContentsData data = prerender_list_.front();
-    prerender_list_.pop_front();
-    data.contents_->Destroy(final_status);
+  while (!active_prerender_list_.empty()) {
+    PrerenderContents* contents = active_prerender_list_.front()->contents_;
+    contents->Destroy(final_status);
   }
   DeletePendingDeleteEntries();
 }
 
 void PrerenderManager::DestroyAndMarkMatchCompleteAsUsed(
     PrerenderContents* prerender_contents,
     FinalStatus final_status) {
   prerender_contents->set_match_complete_status(
       PrerenderContents::MATCH_COMPLETE_REPLACED);
   histograms_->RecordFinalStatus(prerender_contents->origin(),
@@ skipping 38 matching lines @@
   if (!render_process_host || !render_process_host->GetBrowserContext())
     return NULL;
   Profile* profile = Profile::FromBrowserContext(
       render_process_host->GetBrowserContext());
   if (!profile)
     return NULL;
   return PrerenderManagerFactory::GetInstance()->GetForProfile(profile);
 }
 
 }  // namespace prerender
+