Do conservative prerendering based on the LocalPredictor in Dev/Canary.

chrome/browser/prerender/prerender_local_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/prerender/prerender_local_predictor.h"
 
 #include <ctype.h>
 
 #include <algorithm>
 #include <map>
 #include <set>
 #include <string>
 #include <utility>
 
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/timer.h"
 #include "chrome/browser/history/history_database.h"
 #include "chrome/browser/history/history_db_task.h"
 #include "chrome/browser/history/history_service.h"
 #include "chrome/browser/history/history_service_factory.h"
+#include "chrome/browser/prerender/prerender_handle.h"
 #include "chrome/browser/prerender/prerender_histograms.h"
 #include "chrome/browser/prerender/prerender_manager.h"
 #include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/ui/tab_contents/tab_contents_iterator.h"
 #include "content/public/browser/browser_thread.h"
+#include "content/public/browser/navigation_controller.h"
+#include "content/public/browser/session_storage_namespace.h"
+#include "content/public/browser/web_contents.h"
+#include "content/public/browser/web_contents_view.h"
 #include "content/public/common/page_transition_types.h"
 #include "crypto/secure_hash.h"
+#include "googleurl/src/url_canon.h"
 #include "grit/browser_resources.h"
 #include "ui/base/resource/resource_bundle.h"
 
 using content::BrowserThread;
 using content::PageTransition;
+using content::SessionStorageNamespace;
+using content::WebContents;
 using history::URLID;
+using predictors::LoggedInPredictorTable;
+using std::string;
+using std::vector;
 
 namespace prerender {
 
 namespace {
 
 static const size_t kURLHashSize = 5;
+static const int kNumPrerenderCandidates = 5;
+
+}  // namespace
+
+struct PrerenderLocalPredictor::LocalPredictorURLInfo {

[Shishir, 2013/05/07 22:57:30]

Add comment about struct.

[tburkard, 2013/05/07 23:21:59]

Done.

+  URLID id;
+  GURL url;
+  bool url_lookup_success;
+  bool logged_in;
+  bool logged_in_lookup_ok;
+  double priority;
+};
+
+struct PrerenderLocalPredictor::LocalPredictorURLLookupInfo {

[Shishir, 2013/05/07 22:57:30]

Add comments about struct.

[tburkard, 2013/05/07 23:21:59]

Done.

+  LocalPredictorURLInfo source_url_;
+  vector<LocalPredictorURLInfo> candidate_urls_;
+  explicit LocalPredictorURLLookupInfo(URLID source_id) {
+    source_url_.id = source_id;
+  }
+  void MaybeAddCandidateURL(URLID id, double priority) {
+    LocalPredictorURLInfo info;
+    info.id = id;
+    info.priority = priority;
+    int insert_pos = candidate_urls_.size();
+    if (insert_pos < kNumPrerenderCandidates)
+      candidate_urls_.push_back(info);
+    while (insert_pos > 0 &&

[Shishir, 2013/05/07 22:57:30]

Maybe use a list so you can just insert in the right position.

[tburkard, 2013/05/07 23:21:59]

I'd prefer to keep it the way it is for now, since we are just talking about 5
items and this works and is already written. Also these thing will be likely to
be changed in the near future as we experiment further.

[Shishir, 2013/05/08 20:19:20]

I still think this code is messy. Eg. it has the following check three times.
Add a todo if you will leave as is.

if (insert_pos < kNumPrerenderCandidates) 

[tburkard, 2013/05/08 20:35:47]

Done.

+           candidate_urls_[insert_pos - 1].priority < info.priority) {
+      if (insert_pos < kNumPrerenderCandidates)
+        candidate_urls_[insert_pos] = candidate_urls_[insert_pos - 1];
+      insert_pos--;
+    }
+    if (insert_pos < kNumPrerenderCandidates)
+      candidate_urls_[insert_pos] = info;
+  }
+};
+
+namespace {
 
 // Task to lookup the URL for a given URLID.
 class GetURLForURLIDTask : public history::HistoryDBTask {
  public:
-  GetURLForURLIDTask(URLID url_id, base::Callback<void(const GURL&)> callback)
-      : url_id_(url_id),
-        success_(false),
+  GetURLForURLIDTask(PrerenderLocalPredictor::LocalPredictorURLLookupInfo*
+                     request,

[Shishir, 2013/05/07 22:57:30]

indent 4 spaces.

[tburkard, 2013/05/07 23:21:59]

Done.

+                     const base::Closure& callback)
+      : request_(request),
         callback_(callback),
         start_time_(base::Time::Now()) {
   }
 
   virtual bool RunOnDBThread(history::HistoryBackend* backend,
                              history::HistoryDatabase* db) OVERRIDE {
-    history::URLRow url_row;
-    success_ = db->GetURLRow(url_id_, &url_row);
-    if (success_)
-      url_ = url_row.url();
+    DoURLLookup(db, &request_->source_url_);
+    for (int i = 0; i < static_cast<int>(request_->candidate_urls_.size()); i++)
+      DoURLLookup(db, &request_->candidate_urls_[i]);
     return true;
   }
 
   virtual void DoneRunOnMainThread() OVERRIDE {
-    if (success_) {
-      callback_.Run(url_);
-      UMA_HISTOGRAM_CUSTOM_TIMES("Prerender.LocalPredictorURLLookupTime",
-                                 base::Time::Now() - start_time_,
-                                 base::TimeDelta::FromMilliseconds(10),
-                                 base::TimeDelta::FromSeconds(10),
-                                 50);
-    }
+    callback_.Run();
+    UMA_HISTOGRAM_CUSTOM_TIMES("Prerender.LocalPredictorURLLookupTime",
+                               base::Time::Now() - start_time_,
+                               base::TimeDelta::FromMilliseconds(10),
+                               base::TimeDelta::FromSeconds(10),
+                               50);
   }
 
  private:
   virtual ~GetURLForURLIDTask() {}
 
-  URLID url_id_;
-  bool success_;
-  base::Callback<void(const GURL&)> callback_;
+  void DoURLLookup(history::HistoryDatabase* db,
+                   PrerenderLocalPredictor::LocalPredictorURLInfo* request) {
+    history::URLRow url_row;
+    request->url_lookup_success = db->GetURLRow(request->id, &url_row);
+    if (request->url_lookup_success)
+      request->url = url_row.url();
+  }
+
+  PrerenderLocalPredictor::LocalPredictorURLLookupInfo* request_;
+  base::Closure callback_;
   base::Time start_time_;
-  GURL url_;
   DISALLOW_COPY_AND_ASSIGN(GetURLForURLIDTask);
 };
 
 // Task to load history from the visit database on startup.
 class GetVisitHistoryTask : public history::HistoryDBTask {
  public:
   GetVisitHistoryTask(PrerenderLocalPredictor* local_predictor,
                       int max_visits)
       : local_predictor_(local_predictor),
         max_visits_(max_visits),
-        visit_history_(new std::vector<history::BriefVisitInfo>) {
+        visit_history_(new vector<history::BriefVisitInfo>) {
   }
 
   virtual bool RunOnDBThread(history::HistoryBackend* backend,
                              history::HistoryDatabase* db) OVERRIDE {
     db->GetBriefVisitInfoOfMostRecentVisits(max_visits_, visit_history_.get());
     return true;
   }
 
   virtual void DoneRunOnMainThread() OVERRIDE {
     local_predictor_->OnGetInitialVisitHistory(visit_history_.Pass());
   }
 
  private:
   virtual ~GetVisitHistoryTask() {}
 
   PrerenderLocalPredictor* local_predictor_;
   int max_visits_;
-  scoped_ptr<std::vector<history::BriefVisitInfo> > visit_history_;
+  scoped_ptr<vector<history::BriefVisitInfo> > visit_history_;
   DISALLOW_COPY_AND_ASSIGN(GetVisitHistoryTask);
 };
 
 // Maximum visit history to retrieve from the visit database.
 const int kMaxVisitHistory = 100 * 1000;
 
 // Visit history size at which to trigger pruning, and number of items to prune.
 const int kVisitHistoryPruneThreshold = 120 * 1000;
 const int kVisitHistoryPruneAmount = 20 * 1000;
 
-const int kMaxLocalPredictionTimeMs = 300 * 1000;
+const int kMaxLocalPredictionTimeMs = 180 * 1000;
 const int kMinLocalPredictionTimeMs = 500;
 
 bool IsBackForward(PageTransition transition) {
   return (transition & content::PAGE_TRANSITION_FORWARD_BACK) != 0;
 }
 
 bool IsHomePage(PageTransition transition) {
   return (transition & content::PAGE_TRANSITION_HOME_PAGE) != 0;
 }
 
 bool IsIntermediateRedirect(PageTransition transition) {
   return (transition & content::PAGE_TRANSITION_CHAIN_END) == 0;
 }
 
 bool ShouldExcludeTransitionForPrediction(PageTransition transition) {
   return IsBackForward(transition) || IsHomePage(transition) ||
       IsIntermediateRedirect(transition);
 }
 
 base::Time GetCurrentTime() {
   return base::Time::Now();
 }
 
-bool StrCaseStr(std::string haystack, std::string needle) {
+bool StrCaseStr(string haystack, string needle) {

[Shishir, 2013/05/07 22:57:30]

Maybe rename to StringContainsIgnoringCase?

[tburkard, 2013/05/07 23:21:59]

Done.

   std::transform(haystack.begin(), haystack.end(), haystack.begin(), ::tolower);
   std::transform(needle.begin(), needle.end(), needle.begin(), ::tolower);
-  return haystack.find(needle) != std::string::npos;
+  return haystack.find(needle) != string::npos;
 }
 
 bool IsExtendedRootURL(const GURL& url) {
-  const std::string& path = url.path();
+  const string& path = url.path();
   return path == "/index.html" || path == "/home.html" ||
       path == "/main.html" ||
       path == "/index.htm" || path == "/home.htm" || path == "/main.htm" ||
       path == "/index.php" || path == "/home.php" || path == "/main.php" ||
       path == "/index.asp" || path == "/home.asp" || path == "/main.asp" ||
       path == "/index.py" || path == "/home.py" || path == "/main.py" ||
       path == "/index.pl" || path == "/home.pl" || path == "/main.pl";
 }
 
 bool IsRootPageURL(const GURL& url) {
   return (url.path() == "/" || url.path() == "" || IsExtendedRootURL(url)) &&
       (!url.has_query()) && (!url.has_ref());
 }
 
+bool IsLogInURL(const GURL& url) {
+  return StrCaseStr(url.spec().c_str(), "login") ||
+      StrCaseStr(url.spec().c_str(), "signin");
+}
+
+bool IsLogOutURL(const GURL& url) {
+  return StrCaseStr(url.spec().c_str(), "logout") ||
+      StrCaseStr(url.spec().c_str(), "signout");
+}
+
 int64 URLHashToInt64(const unsigned char* data) {
   COMPILE_ASSERT(kURLHashSize < sizeof(int64), url_hash_must_fit_in_int64);
   int64 value = 0;
   memcpy(&value, data, kURLHashSize);
   return value;
 }
 
 int64 GetInt64URLHashForURL(const GURL& url) {
   COMPILE_ASSERT(kURLHashSize < sizeof(int64), url_hash_must_fit_in_int64);
   scoped_ptr<crypto::SecureHash> hash(
       crypto::SecureHash::Create(crypto::SecureHash::SHA256));
   int64 hash_value = 0;
   const char* url_string = url.spec().c_str();
   hash->Update(url_string, strlen(url_string));
   hash->Finish(&hash_value, kURLHashSize);
   return hash_value;
 }
 
+bool URLsIdenticalIgnoringFragments(const GURL& url1, const GURL& url2) {
+  url_canon::Replacements<char> replacement;
+  replacement.ClearRef();
+  GURL u1 = url1.ReplaceComponents(replacement);
+  GURL u2 = url2.ReplaceComponents(replacement);
+  return (u1 == u2);
+}
+
+void LookupLoggedInStatesOnDBThread(
+    scoped_refptr<LoggedInPredictorTable> logged_in_predictor_table,
+    PrerenderLocalPredictor::LocalPredictorURLLookupInfo* request_) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::DB));
+  for (int i = 0; i < static_cast<int>(request_->candidate_urls_.size()); i++) {
+    PrerenderLocalPredictor::LocalPredictorURLInfo* info =
+        &request_->candidate_urls_[i];
+    if (info->url_lookup_success) {
+      logged_in_predictor_table->HasUserLoggedIn(
+          info->url, &info->logged_in, &info->logged_in_lookup_ok);
+    } else {
+      info->logged_in_lookup_ok = false;
+    }
+  }
+}
+
 }  // namespace
 
-struct PrerenderLocalPredictor::PrerenderData {
-  PrerenderData(URLID url_id, const GURL& url, double priority,
+struct PrerenderLocalPredictor::PrerenderProperties {
+  PrerenderProperties(URLID url_id, const GURL& url, double priority,
                 base::Time start_time)
       : url_id(url_id),
         url(url),
         priority(priority),
         start_time(start_time) {
   }
 
   URLID url_id;
   GURL url;
   double priority;
   // For expiration purposes, this is a synthetic start time consisting either
   // of the actual start time, or of the last time the page was re-requested
   // for prerendering - 10 seconds (unless the original request came after
   // that).  This is to emulate the effect of re-prerendering a page that is
   // about to expire, because it was re-requested for prerendering a second
   // time after the actual prerender being kept around.
   base::Time start_time;
   // The actual time this page was last requested for prerendering.
   base::Time actual_start_time;
 
  private:
-  DISALLOW_IMPLICIT_CONSTRUCTORS(PrerenderData);
+  DISALLOW_IMPLICIT_CONSTRUCTORS(PrerenderProperties);
 };
 
 PrerenderLocalPredictor::PrerenderLocalPredictor(
     PrerenderManager* prerender_manager)
     : prerender_manager_(prerender_manager),
-      is_visit_database_observer_(false) {
+      is_visit_database_observer_(false),
+      weak_factory_(this) {
   RecordEvent(EVENT_CONSTRUCTED);
   if (MessageLoop::current()) {
     timer_.Start(FROM_HERE,
                  base::TimeDelta::FromMilliseconds(kInitDelayMs),
                  this,
                  &PrerenderLocalPredictor::Init);
     RecordEvent(EVENT_INIT_SCHEDULED);
   }
 
   static const size_t kChecksumHashSize = 32;
@@ skipping 19 matching lines @@
   for (const unsigned char* p = front + kChecksumHashSize;
        p < front + size;
        p += kURLHashSize) {
     url_whitelist_.insert(URLHashToInt64(p));
   }
   RecordEvent(EVENT_URL_WHITELIST_OK);
 }
 
 PrerenderLocalPredictor::~PrerenderLocalPredictor() {
   Shutdown();
+  if (prerender_handle_.get())
+    prerender_handle_->OnCancel();
 }
 
 void PrerenderLocalPredictor::Shutdown() {
   timer_.Stop();
   if (is_visit_database_observer_) {
     HistoryService* history = GetHistoryIfExists();
     CHECK(history);
     history->RemoveVisitDatabaseObserver(this);
     is_visit_database_observer_ = false;
   }
@@ skipping 26 matching lines @@
     return;
   RecordEvent(EVENT_ADD_VISIT_RELEVANT_TRANSITION);
   base::TimeDelta max_age =
       base::TimeDelta::FromMilliseconds(kMaxLocalPredictionTimeMs);
   base::TimeDelta min_age =
       base::TimeDelta::FromMilliseconds(kMinLocalPredictionTimeMs);
   std::set<URLID> next_urls_currently_found;
   std::map<URLID, int> next_urls_num_found;
   int num_occurrences_of_current_visit = 0;
   base::Time last_visited;
-  URLID best_next_url = 0;
-  int best_next_url_count = 0;
-  const std::vector<history::BriefVisitInfo>& visits = *(visit_history_.get());
+  scoped_ptr<LocalPredictorURLLookupInfo> lookup_info(
+      new LocalPredictorURLLookupInfo(info.url_id));
+  const vector<history::BriefVisitInfo>& visits = *(visit_history_.get());
   for (int i = 0; i < static_cast<int>(visits.size()); i++) {
     if (!ShouldExcludeTransitionForPrediction(visits[i].transition)) {
       if (visits[i].url_id == info.url_id) {
         last_visited = visits[i].time;
         num_occurrences_of_current_visit++;
         next_urls_currently_found.clear();
         continue;
       }
       if (!last_visited.is_null() &&
           last_visited > visits[i].time - max_age &&
           last_visited < visits[i].time - min_age) {
         next_urls_currently_found.insert(visits[i].url_id);
       }
     }
     if (i == static_cast<int>(visits.size()) - 1 ||
         visits[i+1].url_id == info.url_id) {
       for (std::set<URLID>::iterator it = next_urls_currently_found.begin();
            it != next_urls_currently_found.end();
            ++it) {
         std::pair<std::map<URLID, int>::iterator, bool> insert_ret =
             next_urls_num_found.insert(std::pair<URLID, int>(*it, 0));
         std::map<URLID, int>::iterator num_found_it = insert_ret.first;
         num_found_it->second++;
-        if (num_found_it->second > best_next_url_count) {
-          best_next_url_count = num_found_it->second;
-          best_next_url = *it;
-        }
       }
     }
   }
 
-  // Only consider a candidate next page for prerendering if it was viewed
-  // at least twice, and at least 10% of the time.
-  if (num_occurrences_of_current_visit > 0 &&
-      best_next_url_count > 1 &&
-      best_next_url_count * 10 >= num_occurrences_of_current_visit) {
-    RecordEvent(EVENT_ADD_VISIT_IDENTIFIED_PRERENDER_CANDIDATE);
-    double priority = static_cast<double>(best_next_url_count) /
-        static_cast<double>(num_occurrences_of_current_visit);
-    if (ShouldReplaceCurrentPrerender(priority)) {
-      RecordEvent(EVENT_START_URL_LOOKUP);
-      HistoryService* history = GetHistoryIfExists();
-      if (history) {
-        history->ScheduleDBTask(
-            new GetURLForURLIDTask(
-                best_next_url,
-                base::Bind(&PrerenderLocalPredictor::OnLookupURL,
-                           base::Unretained(this),
-                           best_next_url,
-                           priority)),
-            &history_db_consumer_);
-      }
+  for (std::map<URLID, int>::const_iterator it = next_urls_num_found.begin();
+       it != next_urls_num_found.end();
+       ++it) {
+    // Only consider a candidate next page for prerendering if it was viewed
+    // at least twice, and at least 10% of the time.
+    if (num_occurrences_of_current_visit > 0 &&
+        it->second > 1 &&
+        it->second * 10 >= num_occurrences_of_current_visit) {
+      RecordEvent(EVENT_ADD_VISIT_IDENTIFIED_PRERENDER_CANDIDATE);
+      double priority = static_cast<double>(it->second) /
+          static_cast<double>(num_occurrences_of_current_visit);
+      lookup_info->MaybeAddCandidateURL(it->first, priority);
     }
   }
+
+  if (lookup_info->candidate_urls_.size() < 1) {

[Shishir, 2013/05/07 22:57:30]

== 0

[tburkard, 2013/05/07 23:21:59]

Done.

+    RecordEvent(EVENT_NO_PRERENDER_CANDIDATES);
+    return;
+  }
+
+  RecordEvent(EVENT_START_URL_LOOKUP);
+  HistoryService* history = GetHistoryIfExists();
+  if (history) {
+    RecordEvent(EVENT_GOT_HISTORY_ISSUING_LOOKUP);
+    LocalPredictorURLLookupInfo* lookup_info_ptr = lookup_info.get();
+    history->ScheduleDBTask(
+        new GetURLForURLIDTask(
+            lookup_info_ptr,
+            base::Bind(&PrerenderLocalPredictor::OnLookupURL,
+                       base::Unretained(this),

[Shishir, 2013/05/07 22:57:30]

unreatined? What if the predictor is deleted?

[tburkard, 2013/05/07 23:21:59]

The use of the history_db_consumer_ will prevent anything bad from happening in
this case.

+                       base::Passed(&lookup_info))),
+        &history_db_consumer_);
+  }
 }
 
-void PrerenderLocalPredictor::OnLookupURL(history::URLID url_id,
-                                          double priority,
-                                          const GURL& url) {
+void PrerenderLocalPredictor::OnLookupURL(
+    scoped_ptr<LocalPredictorURLLookupInfo> info) {
   RecordEvent(EVENT_PRERENDER_URL_LOOKUP_RESULT);
 
-  base::Time current_time = GetCurrentTime();
-  if (ShouldReplaceCurrentPrerender(priority)) {
-    if (IsRootPageURL(url)) {
-      RecordEvent(EVENT_ADD_VISIT_PRERENDERING);
-      if (current_prerender_.get() && current_prerender_->url_id == url_id) {
-        RecordEvent(EVENT_ADD_VISIT_PRERENDERING_EXTENDED);
-        if (priority > current_prerender_->priority)
-          current_prerender_->priority = priority;
-        // If the prerender already existed, we want to extend it.  However,
-        // we do not want to set its start_time to the current time to
-        // disadvantage PLT computations when the prerender is swapped in.
-        // So we set the new start time to current_time - 10s (since the vast
-        // majority of PLTs are < 10s), provided that is not before the actual
-        // time the prerender was started (so as to not artificially advantage
-        // the PLT computation).
-        base::Time simulated_new_start_time =
-            current_time - base::TimeDelta::FromSeconds(10);
-        if (simulated_new_start_time > current_prerender_->start_time)
-          current_prerender_->start_time = simulated_new_start_time;
-      } else {
-        current_prerender_.reset(
-            new PrerenderData(url_id, url, priority, current_time));
-      }
-      current_prerender_->actual_start_time = current_time;
-    } else {
-      RecordEvent(EVENT_ADD_VISIT_NOT_ROOTPAGE);
+  if (!info->source_url_.url_lookup_success ||
+      !(info->candidate_urls_.size() >= 1) ||

[Shishir, 2013/05/07 22:57:30]

This condition cannot happen, so you can add a dcheck.

[tburkard, 2013/05/07 23:21:59]

Done.

+      !info->candidate_urls_[0].url_lookup_success) {

[Shishir, 2013/05/07 22:57:30]

Cant you use the second candidate if the first's lookup fails?

[tburkard, 2013/05/07 23:21:59]

Done.

+    RecordEvent(EVENT_PRERENDER_URL_LOOKUP_FAILED);
+    return;
+  }
+
+  LogCandidateURLStats(info->candidate_urls_[0].url);
+
+  WebContents* source_web_contents = NULL;
+
+#if !defined(OS_ANDROID)
+  for (TabContentsIterator it; !it.done(); it.Next()) {

[Shishir, 2013/05/07 22:57:30]

Need to document this correctly since this is not straight forward.

[tburkard, 2013/05/07 23:21:59]

Done.

+    if (it->GetURL() == info->source_url_.url) {
+      source_web_contents = *it;
+      break;
     }
   }
+#endif
 
+  if (!source_web_contents) {
+    RecordEvent(EVENT_PRERENDER_URL_LOOKUP_NO_SOURCE_WEBCONTENTS_FOUND);
+    return;
+  }
+
+  scoped_refptr<SessionStorageNamespace> session_storage_namespace =
+      source_web_contents->GetController().GetDefaultSessionStorageNamespace();
+
+  gfx::Rect container_bounds;
+  source_web_contents->GetView()->GetContainerBounds(&container_bounds);
+  scoped_ptr<gfx::Size> size(new gfx::Size(container_bounds.size()));
+
+  scoped_refptr<LoggedInPredictorTable> logged_in_table =
+      prerender_manager_->logged_in_predictor_table();
+
+  if (!logged_in_table.get()) {
+    RecordEvent(EVENT_PRERENDER_URL_LOOKUP_NO_LOGGED_IN_TABLE_FOUND);
+    return;
+  }
+
+  RecordEvent(EVENT_PRERENDER_URL_LOOKUP_ISSUING_LOGGED_IN_LOOKUP);
+
+  LocalPredictorURLLookupInfo* info_ptr = info.get();
+  BrowserThread::PostTaskAndReply(
+      BrowserThread::DB, FROM_HERE,
+      base::Bind(&LookupLoggedInStatesOnDBThread,
+                 logged_in_table,
+                 info_ptr),
+      base::Bind(&PrerenderLocalPredictor::ContinuePrerenderCheck,
+                 weak_factory_.GetWeakPtr(),
+                 session_storage_namespace,
+                 base::Passed(&size),
+                 base::Passed(&info)));
+}
+
+void PrerenderLocalPredictor::LogCandidateURLStats(const GURL& url) const {
   if (url_whitelist_.count(GetInt64URLHashForURL(url)) > 0) {
     RecordEvent(EVENT_PRERENDER_URL_LOOKUP_RESULT_ON_WHITELIST);
     if (IsRootPageURL(url))
       RecordEvent(EVENT_PRERENDER_URL_LOOKUP_RESULT_ON_WHITELIST_ROOT_PAGE);
   }
   if (IsRootPageURL(url))
     RecordEvent(EVENT_PRERENDER_URL_LOOKUP_RESULT_ROOT_PAGE);
   if (IsExtendedRootURL(url))
     RecordEvent(EVENT_PRERENDER_URL_LOOKUP_RESULT_EXTENDED_ROOT_PAGE);
   if (IsRootPageURL(url) && url.SchemeIs("http"))
     RecordEvent(EVENT_PRERENDER_URL_LOOKUP_RESULT_ROOT_PAGE_HTTP);
   if (url.SchemeIs("http"))
     RecordEvent(EVENT_PRERENDER_URL_LOOKUP_RESULT_IS_HTTP);
   if (url.has_query())
     RecordEvent(EVENT_PRERENDER_URL_LOOKUP_RESULT_HAS_QUERY_STRING);
-  if (StrCaseStr(url.spec().c_str(), "logout") ||
-      StrCaseStr(url.spec().c_str(), "signout"))
+  if (IsLogOutURL(url))
     RecordEvent(EVENT_PRERENDER_URL_LOOKUP_RESULT_CONTAINS_LOGOUT);
-  if (StrCaseStr(url.spec().c_str(), "login") ||
-      StrCaseStr(url.spec().c_str(), "signin"))
+  if (IsLogInURL(url))
     RecordEvent(EVENT_PRERENDER_URL_LOOKUP_RESULT_CONTAINS_LOGIN);
 }
 
 void PrerenderLocalPredictor::OnGetInitialVisitHistory(
-    scoped_ptr<std::vector<history::BriefVisitInfo> > visit_history) {
+    scoped_ptr<vector<history::BriefVisitInfo> > visit_history) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DCHECK(!visit_history_.get());
   RecordEvent(EVENT_INIT_SUCCEEDED);
   // Since the visit history has descending timestamps, we must reverse it.
-  visit_history_.reset(new std::vector<history::BriefVisitInfo>(
+  visit_history_.reset(new vector<history::BriefVisitInfo>(
       visit_history->rbegin(), visit_history->rend()));
 }
 
 HistoryService* PrerenderLocalPredictor::GetHistoryIfExists() const {
   Profile* profile = prerender_manager_->profile();
   if (!profile)
     return NULL;
   return HistoryServiceFactory::GetForProfileWithoutCreating(profile);
 }
 
 void PrerenderLocalPredictor::Init() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   RecordEvent(EVENT_INIT_STARTED);
   HistoryService* history = GetHistoryIfExists();
   if (history) {
     CHECK(!is_visit_database_observer_);
     history->ScheduleDBTask(
         new GetVisitHistoryTask(this, kMaxVisitHistory),
         &history_db_consumer_);
     history->AddVisitDatabaseObserver(this);
     is_visit_database_observer_ = true;
   } else {
     RecordEvent(EVENT_INIT_FAILED_NO_HISTORY);
   }
 }
 
 void PrerenderLocalPredictor::OnPLTEventForURL(const GURL& url,
                                                base::TimeDelta page_load_time) {
-  scoped_ptr<PrerenderData> prerender;
+  scoped_ptr<PrerenderProperties> prerender;
   if (DoesPrerenderMatchPLTRecord(last_swapped_in_prerender_.get(),
                                   url, page_load_time)) {
     prerender.reset(last_swapped_in_prerender_.release());
   }
   if (DoesPrerenderMatchPLTRecord(current_prerender_.get(),
                                   url, page_load_time)) {
     prerender.reset(current_prerender_.release());
   }
   if (!prerender.get())
     return;
@@ skipping 12 matching lines @@
       UMA_HISTOGRAM_CUSTOM_TIMES("Prerender.SimulatedLocalBrowsingPLT",
                                  new_plt,
                                  base::TimeDelta::FromMilliseconds(10),
                                  base::TimeDelta::FromSeconds(60),
                                  100);
     }
   }
 }
 
 bool PrerenderLocalPredictor::IsPrerenderStillValid(
-    PrerenderLocalPredictor::PrerenderData* prerender) const {
+    PrerenderLocalPredictor::PrerenderProperties* prerender) const {
   return (prerender &&
           (prerender->start_time +
            base::TimeDelta::FromMilliseconds(kMaxLocalPredictionTimeMs))
           > GetCurrentTime());
 }
 
 void PrerenderLocalPredictor::RecordEvent(
     PrerenderLocalPredictor::Event event) const {
   UMA_HISTOGRAM_ENUMERATION("Prerender.LocalPredictorEvent",
       event, PrerenderLocalPredictor::EVENT_MAX_VALUE);
 }
 
 bool PrerenderLocalPredictor::DoesPrerenderMatchPLTRecord(
-    PrerenderData* prerender, const GURL& url, base::TimeDelta plt) const {
+    PrerenderProperties* prerender,
+    const GURL& url,
+    base::TimeDelta plt) const {
   if (prerender && prerender->start_time < GetCurrentTime() - plt) {
     if (prerender->url.is_empty())
       RecordEvent(EVENT_ERROR_NO_PRERENDER_URL_FOR_PLT);
     return (prerender->url == url);
   } else {
     return false;
   }
 }
 
 bool PrerenderLocalPredictor::ShouldReplaceCurrentPrerender(
     double priority) const {
-  base::TimeDelta max_age =
-      base::TimeDelta::FromMilliseconds(kMaxLocalPredictionTimeMs);
-  return (!current_prerender_.get()) ||
-    current_prerender_->priority < priority ||
-    current_prerender_->start_time < GetCurrentTime() - max_age;
+  return (!prerender_handle_.get() ||
+          !prerender_handle_->IsPrerendering() ||
+          current_prerender_priority_ < priority);
+}
+
+void PrerenderLocalPredictor::ContinuePrerenderCheck(
+    scoped_refptr<SessionStorageNamespace> session_storage_namespace,
+    scoped_ptr<gfx::Size> size,
+    scoped_ptr<LocalPredictorURLLookupInfo> info) {
+  RecordEvent(EVENT_CONTINUE_PRERENDER_CHECK_STARTED);
+  scoped_ptr<LocalPredictorURLInfo> url_info;
+  for (int i = 0; i < static_cast<int>(info->candidate_urls_.size()); i++) {
+    url_info.reset(new LocalPredictorURLInfo(info->candidate_urls_[i]));
+    if (!url_info->url_lookup_success) {
+      RecordEvent(EVENT_CONTINUE_PRERENDER_CHECK_NO_URL);
+      url_info.reset(NULL);
+      continue;
+    }
+    if (!ShouldReplaceCurrentPrerender(url_info->priority)) {
+      RecordEvent(EVENT_CONTINUE_PRERENDER_CHECK_PRIORITY_TOO_LOW);
+      url_info.reset(NULL);
+      continue;
+    }
+    if (URLsIdenticalIgnoringFragments(info->source_url_.url,
+                                       url_info->url)) {
+      RecordEvent(EVENT_CONTINUE_PRERENDER_CHECK_URLS_IDENTICAL_BUT_FRAGMENT);
+      url_info.reset(NULL);
+      continue;
+    }
+    if (url_info->url.SchemeIs("https")) {
+      RecordEvent(EVENT_CONTINUE_PRERENDER_CHECK_HTTPS);
+      url_info.reset(NULL);
+      continue;
+    }
+    if (IsRootPageURL(url_info->url)) {
+      RecordEvent(EVENT_CONTINUE_PRERENDER_CHECK_ROOT_PAGE);
+      break;

[Shishir, 2013/05/07 22:57:30]

Why is this case different? Documentation?

[tburkard, 2013/05/07 23:21:59]

Done.

+    }
+    if (IsLogOutURL(url_info->url)) {
+      RecordEvent(EVENT_CONTINUE_PRERENDER_CHECK_LOGOUT_URL);
+      url_info.reset(NULL);
+      continue;
+    }
+    if (IsLogInURL(url_info->url)) {
+      RecordEvent(EVENT_CONTINUE_PRERENDER_CHECK_LOGIN_URL);
+      url_info.reset(NULL);
+      continue;
+    }
+    if (!url_info->logged_in && url_info->logged_in_lookup_ok) {
+      RecordEvent(EVENT_CONTINUE_PRERENDER_CHECK_NOT_LOGGED_IN);

[Shishir, 2013/05/07 22:57:30]

Shouldn't this be checked early?

[tburkard, 2013/05/07 23:21:59]

Done.

[tburkard, 2013/05/08 00:25:27]

Sorry, didn't properly reply to this. No, the location of the check is just
right: we want to prerender root pages even for logged in users, and we don't
want to prerender URLs which contain "login/logout" for any users. Ditto https
and fragments. That's why these other checks come first, since they prescribe an
action independent of logged in state.

On 2013/05/07 22:57:30, Shishir wrote:

[Shishir, 2013/05/08 20:19:20]

Since the sequence of checks is to a certain logic, can you write a comment in
this regard before the checks begin.

[tburkard, 2013/05/08 20:35:47]

Done.

+      break;
+    }
+    RecordEvent(EVENT_CONTINUE_PRERENDER_CHECK_FALLTHROUGH_NOT_PRERENDERING);
+    url_info.reset(NULL);
+  }
+  if (!url_info.get())
+    return;
+  RecordEvent(EVENT_CONTINUE_PRERENDER_CHECK_ISSUING_PRERENDER);
+  IssuePrerender(session_storage_namespace, size.Pass(),
+                 url_info.Pass());
+}
+
+void PrerenderLocalPredictor::IssuePrerender(
+    scoped_refptr<SessionStorageNamespace> session_storage_namespace,
+    scoped_ptr<gfx::Size> size,
+    scoped_ptr<LocalPredictorURLInfo> info) {
+  URLID url_id = info->id;
+  const GURL& url = info->url;
+  double priority = info->priority;
+  base::Time current_time = GetCurrentTime();
+  RecordEvent(EVENT_ISSUING_PRERENDER);
+
+  current_prerender_priority_ = priority;
+  scoped_ptr<prerender::PrerenderHandle> old_prerender_handle(
+      prerender_handle_.release());
+  prerender_handle_.reset(prerender_manager_->AddPrerenderFromLocalPredictor(
+      url, session_storage_namespace.get(), *size));
+  if (old_prerender_handle)
+    old_prerender_handle->OnCancel();
+
+  RecordEvent(EVENT_ADD_VISIT_PRERENDERING);
+  if (current_prerender_.get() && current_prerender_->url_id == url_id) {
+    RecordEvent(EVENT_ADD_VISIT_PRERENDERING_EXTENDED);
+    if (priority > current_prerender_->priority)
+      current_prerender_->priority = priority;
+    // If the prerender already existed, we want to extend it.  However,
+    // we do not want to set its start_time to the current time to
+    // disadvantage PLT computations when the prerender is swapped in.
+    // So we set the new start time to current_time - 10s (since the vast
+    // majority of PLTs are < 10s), provided that is not before the actual
+    // time the prerender was started (so as to not artificially advantage
+    // the PLT computation).
+    base::Time simulated_new_start_time =
+        current_time - base::TimeDelta::FromSeconds(10);
+    if (simulated_new_start_time > current_prerender_->start_time)
+      current_prerender_->start_time = simulated_new_start_time;
+  } else {
+    current_prerender_.reset(
+        new PrerenderProperties(url_id, url, priority, current_time));
+  }
+  current_prerender_->actual_start_time = current_time;
 }
 
 }  // namespace prerender