Modifying prefetch to account for multi-profile.

chrome/browser/net/predictor_api.cc

Index: chrome/browser/net/predictor_api.cc
===================================================================
--- chrome/browser/net/predictor_api.cc	(revision 96503)
+++ chrome/browser/net/predictor_api.cc	(working copy)
@@ -1,651 +0,0 @@
-// Copyright (c) 2011 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/net/predictor_api.h"
-
-#include <map>
-#include <string>
-
-#include "base/lazy_instance.h"
-#include "base/metrics/field_trial.h"
-#include "base/stl_util.h"
-#include "base/string_number_conversions.h"
-#include "base/synchronization/waitable_event.h"
-#include "base/threading/thread.h"
-#include "base/values.h"
-#include "chrome/browser/browser_process.h"
-#include "chrome/browser/io_thread.h"
-#include "chrome/browser/net/preconnect.h"
-#include "chrome/browser/net/referrer.h"
-#include "chrome/browser/net/url_info.h"
-#include "chrome/browser/prefs/browser_prefs.h"
-#include "chrome/browser/prefs/pref_service.h"
-#include "chrome/browser/prefs/scoped_user_pref_update.h"
-#include "chrome/browser/prefs/session_startup_pref.h"
-#include "chrome/browser/profiles/profile.h"
-#include "chrome/browser/ui/browser.h"
-#include "chrome/common/chrome_notification_types.h"
-#include "chrome/common/pref_names.h"
-#include "content/browser/browser_thread.h"
-#include "content/common/notification_registrar.h"
-#include "content/common/notification_service.h"
-#include "net/base/host_resolver.h"
-#include "net/base/host_resolver_impl.h"
-
-using base::Time;
-using base::TimeDelta;
-
-namespace chrome_browser_net {
-
-static void DnsPrefetchMotivatedList(const UrlList& urls,
-                                     UrlInfo::ResolutionMotivation motivation);
-
-static UrlList GetPredictedUrlListAtStartup(PrefService* user_prefs,
-                                            PrefService* local_state);
-
-// Given that the underlying Chromium resolver defaults to a total maximum of
-// 8 paralell resolutions, we will avoid any chance of starving navigational
-// resolutions by limiting the number of paralell speculative resolutions.
-// TODO(jar): Move this limitation into the resolver.
-// static
-const size_t PredictorInit::kMaxSpeculativeParallelResolves = 3;
-
-// To control our congestion avoidance system, which discards a queue when
-// resolutions are "taking too long," we need an expected resolution time.
-// Common average is in the range of 300-500ms.
-static const int kExpectedResolutionTimeMs = 500;
-
-// To control the congestion avoidance system, we need an estimate of how many
-// speculative requests may arrive at once.  Since we currently only keep 8
-// subresource names for each frame, we'll use that as our basis.  Note that
-// when scanning search results lists, we might actually get 10 at a time, and
-// wikipedia can often supply (during a page scan) upwards of 50.  In those odd
-// cases, we may discard some of the later speculative requests mistakenly
-// assuming that the resolutions took too long.
-static const int kTypicalSpeculativeGroupSize = 8;
-
-// The next constant specifies an amount of queueing delay that is "too large,"
-// and indicative of problems with resolutions (perhaps due to an overloaded
-// router, or such).  When we exceed this delay, congestion avoidance will kick
-// in and all speculations in the queue will be discarded.
-// static
-const int PredictorInit::kMaxSpeculativeResolveQueueDelayMs =
-    (kExpectedResolutionTimeMs * kTypicalSpeculativeGroupSize) /
-    kMaxSpeculativeParallelResolves;
-
-// A version number for prefs that are saved. This should be incremented when
-// we change the format so that we discard old data.
-static const int kPredictorStartupFormatVersion = 1;
-
-// There will only be one instance ever created of the following Observer class.
-// The InitialObserver lives on the IO thread, and monitors navigations made by
-// the network stack.  This is only used to identify startup time resolutions
-// (for re-resolution during our next process startup).
-// TODO(jar): Consider preconnecting at startup, which may be faster than
-// waiting for render process to start and request a connection.
-class InitialObserver {
- public:
-  // Recording of when we observed each navigation.
-  typedef std::map<GURL, base::TimeTicks> FirstNavigations;
-
-  // Potentially add a new URL to our startup list.
-  void Append(const GURL& url);
-
-  // Get an HTML version of our current planned first_navigations_.
-  void GetFirstResolutionsHtml(std::string* output);
-
-  // Persist the current first_navigations_ for storage in a list.
-  void GetInitialDnsResolutionList(ListValue* startup_list);
-
-  // Discards all initial loading history.
-  void DiscardInitialNavigationHistory() { first_navigations_.clear(); }
-
- private:
-  // List of the first N URL resolutions observed in this run.
-  FirstNavigations first_navigations_;
-
-  // The number of URLs we'll save for pre-resolving at next startup.
-  static const size_t kStartupResolutionCount = 10;
-};
-
-// TODO(willchan): Look at killing this global.
-static InitialObserver* g_initial_observer = NULL;
-
-//------------------------------------------------------------------------------
-// This section contains all the globally accessable API entry points for the
-// DNS Prefetching feature.
-//------------------------------------------------------------------------------
-
-// Status of speculative DNS resolution and speculative TCP/IP connection
-// feature.
-static bool predictor_enabled = true;
-
-// Cached inverted copy of the off_the_record pref.
-static bool on_the_record_switch = true;
-
-// Enable/disable Dns prefetch activity (either via command line, or via pref).
-void EnablePredictor(bool enable) {
-  // NOTE: this is invoked on the UI thread.
-  predictor_enabled = enable;
-}
-
-void OnTheRecord(bool enable) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  if (on_the_record_switch == enable)
-    return;
-  on_the_record_switch = enable;
-  if (on_the_record_switch)
-    g_browser_process->io_thread()->ChangedToOnTheRecord();
-}
-
-void DiscardInitialNavigationHistory() {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (g_initial_observer)
-    g_initial_observer->DiscardInitialNavigationHistory();
-}
-
-void RegisterUserPrefs(PrefService* user_prefs) {
-  user_prefs->RegisterListPref(prefs::kDnsPrefetchingStartupList,
-                               PrefService::UNSYNCABLE_PREF);
-  user_prefs->RegisterListPref(prefs::kDnsPrefetchingHostReferralList,
-                               PrefService::UNSYNCABLE_PREF);
-}
-
-// When enabled, we use the following instance to service all requests in the
-// browser process.
-// TODO(willchan): Look at killing this.
-static Predictor* g_predictor = NULL;
-
-// This API is only used in the browser process.
-// It is called from an IPC message originating in the renderer.  It currently
-// includes both Page-Scan, and Link-Hover prefetching.
-// TODO(jar): Separate out link-hover prefetching, and page-scan results.
-void DnsPrefetchList(const NameList& hostnames) {
-  // TODO(jar): Push GURL transport further back into renderer, but this will
-  // require a Webkit change in the observer :-/.
-  UrlList urls;
-  for (NameList::const_iterator it = hostnames.begin();
-       it < hostnames.end();
-       ++it) {
-    urls.push_back(GURL("http://" + *it + ":80"));
-  }
-
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  DnsPrefetchMotivatedList(urls, UrlInfo::PAGE_SCAN_MOTIVATED);
-}
-
-static void DnsPrefetchMotivatedList(
-    const UrlList& urls,
-    UrlInfo::ResolutionMotivation motivation) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI) ||
-         BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (!predictor_enabled || NULL == g_predictor)
-    return;
-
-  if (BrowserThread::CurrentlyOn(BrowserThread::IO)) {
-    g_predictor->ResolveList(urls, motivation);
-  } else {
-    BrowserThread::PostTask(
-        BrowserThread::IO,
-        FROM_HERE,
-        NewRunnableMethod(g_predictor,
-                          &Predictor::ResolveList, urls, motivation));
-  }
-}
-
-// This API is used by the autocomplete popup box (where URLs are typed).
-void AnticipateOmniboxUrl(const GURL& url, bool preconnectable) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  if (!predictor_enabled || NULL == g_predictor)
-    return;
-  if (!url.is_valid() || !url.has_host())
-    return;
-
-  g_predictor->AnticipateOmniboxUrl(url, preconnectable);
-}
-
-void PreconnectUrlAndSubresources(const GURL& url) {
-  if (!predictor_enabled || NULL == g_predictor)
-    return;
-  if (!url.is_valid() || !url.has_host())
-    return;
-
-  g_predictor->PreconnectUrlAndSubresources(url);
-}
-
-
-//------------------------------------------------------------------------------
-// This section intermingles prefetch results with actual browser HTTP
-// network activity.  It supports calculating of the benefit of a prefetch, as
-// well as recording what prefetched hostname resolutions might be potentially
-// helpful during the next chrome-startup.
-//------------------------------------------------------------------------------
-
-void PredictFrameSubresources(const GURL& url) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (!predictor_enabled || NULL == g_predictor)
-    return;
-  g_predictor->PredictFrameSubresources(url);
-}
-
-void LearnAboutInitialNavigation(const GURL& url) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (!predictor_enabled || NULL == g_initial_observer )
-    return;
-  g_initial_observer->Append(url);
-}
-
-void LearnFromNavigation(const GURL& referring_url, const GURL& target_url) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (!predictor_enabled || NULL == g_predictor)
-    return;
-  g_predictor->LearnFromNavigation(referring_url, target_url);
-}
-
-// The observer class needs to connect starts and finishes of HTTP network
-// resolutions.  We use the following type for that map.
-typedef std::map<int, UrlInfo> ObservedResolutionMap;
-
-//------------------------------------------------------------------------------
-// Member definitions for InitialObserver class.
-
-void InitialObserver::Append(const GURL& url) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-
-  if (!on_the_record_switch || NULL == g_predictor)
-    return;
-  if (kStartupResolutionCount <= first_navigations_.size())
-    return;
-
-  DCHECK(url.SchemeIs("http") || url.SchemeIs("https"));
-  DCHECK_EQ(url, Predictor::CanonicalizeUrl(url));
-  if (first_navigations_.find(url) == first_navigations_.end())
-    first_navigations_[url] = base::TimeTicks::Now();
-}
-
-void InitialObserver::GetInitialDnsResolutionList(ListValue* startup_list) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  DCHECK(startup_list);
-  startup_list->Clear();
-  DCHECK_EQ(0u, startup_list->GetSize());
-  startup_list->Append(
-      new base::FundamentalValue(kPredictorStartupFormatVersion));
-  for (FirstNavigations::iterator it = first_navigations_.begin();
-       it != first_navigations_.end();
-       ++it) {
-    DCHECK(it->first == Predictor::CanonicalizeUrl(it->first));
-    startup_list->Append(new StringValue(it->first.spec()));
-  }
-}
-
-void InitialObserver::GetFirstResolutionsHtml(std::string* output) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-
-  UrlInfo::UrlInfoTable resolution_list;
-  {
-    for (FirstNavigations::iterator it(first_navigations_.begin());
-         it != first_navigations_.end();
-         it++) {
-      UrlInfo info;
-      info.SetUrl(it->first);
-      info.set_time(it->second);
-      resolution_list.push_back(info);
-    }
-  }
-  UrlInfo::GetHtmlTable(resolution_list,
-      "Future startups will prefetch DNS records for ", false, output);
-}
-
-//------------------------------------------------------------------------------
-// Support observer to detect opening and closing of OffTheRecord windows.
-// This object lives on the UI thread.
-
-class OffTheRecordObserver : public NotificationObserver {
- public:
-  void Register() {
-    // TODO(pkasting): This test should not be necessary.  See crbug.com/12475.
-    if (registrar_.IsEmpty()) {
-      registrar_.Add(this, chrome::NOTIFICATION_BROWSER_CLOSED,
-                     NotificationService::AllSources());
-      registrar_.Add(this, chrome::NOTIFICATION_BROWSER_OPENED,
-                     NotificationService::AllSources());
-    }
-  }
-
-  void Observe(int type, const NotificationSource& source,
-               const NotificationDetails& details) {
-    switch (type) {
-      case chrome::NOTIFICATION_BROWSER_OPENED:
-        if (!Source<Browser>(source)->profile()->IsOffTheRecord())
-          break;
-        ++count_off_the_record_windows_;
-        OnTheRecord(false);
-        break;
-
-      case chrome::NOTIFICATION_BROWSER_CLOSED:
-        if (!Source<Browser>(source)->profile()->IsOffTheRecord())
-        break;  // Ignore ordinary windows.
-        DCHECK_LT(0, count_off_the_record_windows_);
-        if (0 >= count_off_the_record_windows_)  // Defensive coding.
-          break;
-        if (--count_off_the_record_windows_)
-          break;  // Still some windows are incognito.
-        OnTheRecord(true);
-        break;
-
-      default:
-        break;
-    }
-  }
-
- private:
-  friend struct base::DefaultLazyInstanceTraits<OffTheRecordObserver>;
-
-  OffTheRecordObserver() : count_off_the_record_windows_(0) {}
-  ~OffTheRecordObserver() {}
-
-  NotificationRegistrar registrar_;
-  int count_off_the_record_windows_;
-
-  DISALLOW_COPY_AND_ASSIGN(OffTheRecordObserver);
-};
-
-static base::LazyInstance<OffTheRecordObserver> g_off_the_record_observer(
-    base::LINKER_INITIALIZED);
-
-//------------------------------------------------------------------------------
-// This section supports the about:dns page.
-//------------------------------------------------------------------------------
-
-// Provide global support for the about:dns page.
-void PredictorGetHtmlInfo(std::string* output) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-
-  if (!predictor_enabled  || NULL == g_predictor) {
-    output->append("DNS pre-resolution and TCP pre-connection is disabled.");
-  } else {
-    if (!on_the_record_switch) {
-      output->append("Incognito mode is active in a window.");
-    } else {
-      // List items fetched at startup.
-      if (g_initial_observer)
-        g_initial_observer->GetFirstResolutionsHtml(output);
-      // Show list of subresource predictions and stats.
-      g_predictor->GetHtmlReferrerLists(output);
-      // Show list of prediction results.
-      g_predictor->GetHtmlInfo(output);
-    }
-  }
-}
-
-void ClearPredictorCache() {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  if (!predictor_enabled || NULL == g_predictor)
-    return;
-  g_predictor->DiscardAllResults();
-}
-
-//------------------------------------------------------------------------------
-// This section intializes global DNS prefetch services.
-//------------------------------------------------------------------------------
-
-static void InitNetworkPredictor(TimeDelta max_dns_queue_delay,
-                                 size_t max_parallel_resolves,
-                                 PrefService* user_prefs,
-                                 PrefService* local_state,
-                                 bool preconnect_enabled) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
-  bool prefetching_enabled =
-      user_prefs->GetBoolean(prefs::kNetworkPredictionEnabled);
-
-  // Gather the list of hostnames to prefetch on startup.
-  UrlList urls =
-      GetPredictedUrlListAtStartup(user_prefs, local_state);
-
-  ListValue* referral_list =
-      static_cast<ListValue*>(user_prefs->GetList(
-          prefs::kDnsPrefetchingHostReferralList)->DeepCopy());
-
-  // Remove obsolete preferences from local state if necessary.
-  int current_version =
-      local_state->GetInteger(prefs::kMultipleProfilePrefMigration);
-  if ((current_version & browser::DNS_PREFS) == 0) {
-    local_state->RegisterListPref(prefs::kDnsStartupPrefetchList,
-                                  PrefService::UNSYNCABLE_PREF);
-    local_state->RegisterListPref(prefs::kDnsHostReferralList,
-                                  PrefService::UNSYNCABLE_PREF);
-    local_state->ClearPref(prefs::kDnsStartupPrefetchList);
-    local_state->ClearPref(prefs::kDnsHostReferralList);
-    local_state->SetInteger(prefs::kMultipleProfilePrefMigration,
-        current_version | browser::DNS_PREFS);
-  }
-
-  g_browser_process->io_thread()->InitNetworkPredictor(
-      prefetching_enabled, max_dns_queue_delay, max_parallel_resolves, urls,
-      referral_list, preconnect_enabled);
-}
-
-void FinalizePredictorInitialization(
-    Predictor* global_predictor,
-    const UrlList& startup_urls,
-    ListValue* referral_list) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  g_predictor = global_predictor;
-  g_initial_observer = new InitialObserver();
-
-  // Prefetch these hostnames on startup.
-  DnsPrefetchMotivatedList(startup_urls,
-                           UrlInfo::STARTUP_LIST_MOTIVATED);
-  g_predictor->DeserializeReferrersThenDelete(referral_list);
-}
-
-void FreePredictorResources() {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  g_predictor = NULL;  // Owned and released by io_thread.cc.
-  delete g_initial_observer;
-  g_initial_observer = NULL;
-}
-
-//------------------------------------------------------------------------------
-// Functions to handle saving of hostnames from one session to the next, to
-// expedite startup times.
-
-static void SaveDnsPrefetchStateForNextStartupAndTrimOnIOThread(
-    ListValue* startup_list,
-    ListValue* referral_list,
-    base::WaitableEvent* completion) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-
-  if (NULL == g_predictor) {
-    completion->Signal();
-    return;
-  }
-
-  if (g_initial_observer)
-    g_initial_observer->GetInitialDnsResolutionList(startup_list);
-
-  // Do at least one trim at shutdown, in case the user wasn't running long
-  // enough to do any regular trimming of referrers.
-  g_predictor->TrimReferrersNow();
-  g_predictor->SerializeReferrers(referral_list);
-
-  completion->Signal();
-}
-
-void SavePredictorStateForNextStartupAndTrim(PrefService* prefs) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
-  if (!predictor_enabled || g_predictor == NULL)
-    return;
-
-  base::WaitableEvent completion(true, false);
-
-  ListPrefUpdate update_startup_list(prefs, prefs::kDnsPrefetchingStartupList);
-  ListPrefUpdate update_referral_list(prefs,
-                                      prefs::kDnsPrefetchingHostReferralList);
-  bool posted = BrowserThread::PostTask(
-      BrowserThread::IO,
-      FROM_HERE,
-      NewRunnableFunction(SaveDnsPrefetchStateForNextStartupAndTrimOnIOThread,
-          update_startup_list.Get(),
-          update_referral_list.Get(),
-          &completion));
-
-  // TODO(jar): Synchronous waiting for the IO thread is a potential source
-  // to deadlocks and should be investigated. See http://crbug.com/78451.
-  DCHECK(posted);
-  if (posted)
-    completion.Wait();
-}
-
-static UrlList GetPredictedUrlListAtStartup(PrefService* user_prefs,
-                                            PrefService* local_state) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  UrlList urls;
-  // Recall list of URLs we learned about during last session.
-  // This may catch secondary hostnames, pulled in by the homepages.  It will
-  // also catch more of the "primary" home pages, since that was (presumably)
-  // rendered first (and will be rendered first this time too).
-  const ListValue* startup_list =
-      user_prefs->GetList(prefs::kDnsPrefetchingStartupList);
-
-  if (startup_list) {
-    ListValue::const_iterator it = startup_list->begin();
-    int format_version = -1;
-    if (it != startup_list->end() &&
-        (*it)->GetAsInteger(&format_version) &&
-        format_version == kPredictorStartupFormatVersion) {
-      ++it;
-      for (; it != startup_list->end(); ++it) {
-        std::string url_spec;
-        if (!(*it)->GetAsString(&url_spec)) {
-          LOG(DFATAL);
-          break;  // Format incompatibility.
-        }
-        GURL url(url_spec);
-        if (!url.has_host() || !url.has_scheme()) {
-          LOG(DFATAL);
-          break;  // Format incompatibility.
-        }
-
-        urls.push_back(url);
-      }
-    }
-  }
-
-  // Prepare for any static home page(s) the user has in prefs.  The user may
-  // have a LOT of tab's specified, so we may as well try to warm them all.
-  SessionStartupPref tab_start_pref =
-      SessionStartupPref::GetStartupPref(user_prefs);
-  if (SessionStartupPref::URLS == tab_start_pref.type) {
-    for (size_t i = 0; i < tab_start_pref.urls.size(); i++) {
-      GURL gurl = tab_start_pref.urls[i];
-      if (!gurl.is_valid() || gurl.SchemeIsFile() || gurl.host().empty())
-        continue;
-      if (gurl.SchemeIs("http") || gurl.SchemeIs("https"))
-        urls.push_back(gurl.GetWithEmptyPath());
-    }
-  }
-
-  if (urls.empty())
-    urls.push_back(GURL("http://www.google.com:80"));
-
-  return urls;
-}
-
-//------------------------------------------------------------------------------
-// Methods for the helper class that is used to startup and teardown the whole
-// g_predictor system (both DNS pre-resolution and TCP/IP pre-connection).
-
-PredictorInit::PredictorInit(PrefService* user_prefs,
-                             PrefService* local_state,
-                             bool preconnect_enabled) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  // Set up a field trial to see what disabling DNS pre-resolution does to
-  // latency of page loads.
-  base::FieldTrial::Probability kDivisor = 1000;
-  // For each option (i.e., non-default), we have a fixed probability.
-  base::FieldTrial::Probability kProbabilityPerGroup = 1;  // 0.1% probability.
-
-  // After June 30, 2011 builds, it will always be in default group
-  // (default_enabled_prefetch).
-  trial_ = new base::FieldTrial("DnsImpact", kDivisor,
-                                "default_enabled_prefetch", 2011, 10, 30);
-
-  // First option is to disable prefetching completely.
-  int disabled_prefetch = trial_->AppendGroup("disabled_prefetch",
-                                              kProbabilityPerGroup);
-
-  // We're running two experiments at the same time.  The first set of trials
-  // modulates the delay-time until we declare a congestion event (and purge
-  // our queue).  The second modulates the number of concurrent resolutions
-  // we do at any time.  Users are in exactly one trial (or the default) during
-  // any one run, and hence only one experiment at a time.
-  // Experiment 1:
-  // Set congestion detection at 250, 500, or 750ms, rather than the 1 second
-  // default.
-  int max_250ms_prefetch = trial_->AppendGroup("max_250ms_queue_prefetch",
-                                               kProbabilityPerGroup);
-  int max_500ms_prefetch = trial_->AppendGroup("max_500ms_queue_prefetch",
-                                               kProbabilityPerGroup);
-  int max_750ms_prefetch = trial_->AppendGroup("max_750ms_queue_prefetch",
-                                               kProbabilityPerGroup);
-  // Set congestion detection at 2 seconds instead of the 1 second default.
-  int max_2s_prefetch = trial_->AppendGroup("max_2s_queue_prefetch",
-                                            kProbabilityPerGroup);
-  // Experiment 2:
-  // Set max simultaneous resoultions to 2, 4, or 6, and scale the congestion
-  // limit proportionally (so we don't impact average probability of asserting
-  // congesion very much).
-  int max_2_concurrent_prefetch = trial_->AppendGroup(
-      "max_2 concurrent_prefetch", kProbabilityPerGroup);
-  int max_4_concurrent_prefetch = trial_->AppendGroup(
-      "max_4 concurrent_prefetch", kProbabilityPerGroup);
-  int max_6_concurrent_prefetch = trial_->AppendGroup(
-      "max_6 concurrent_prefetch", kProbabilityPerGroup);
-
-  // We will register the incognito observer regardless of whether prefetching
-  // is enabled, as it is also used to clear the host cache.
-  g_off_the_record_observer.Get().Register();
-
-  if (trial_->group() != disabled_prefetch) {
-    // Initialize the DNS prefetch system.
-    size_t max_parallel_resolves = kMaxSpeculativeParallelResolves;
-    int max_queueing_delay_ms = kMaxSpeculativeResolveQueueDelayMs;
-
-    if (trial_->group() == max_2_concurrent_prefetch)
-      max_parallel_resolves = 2;
-    else if (trial_->group() == max_4_concurrent_prefetch)
-      max_parallel_resolves = 4;
-    else if (trial_->group() == max_6_concurrent_prefetch)
-      max_parallel_resolves = 6;
-
-    if (trial_->group() == max_250ms_prefetch) {
-      max_queueing_delay_ms =
-         (250 * kTypicalSpeculativeGroupSize) /  max_parallel_resolves;
-    } else if (trial_->group() == max_500ms_prefetch) {
-      max_queueing_delay_ms =
-          (500 * kTypicalSpeculativeGroupSize) /  max_parallel_resolves;
-    } else if (trial_->group() == max_750ms_prefetch) {
-      max_queueing_delay_ms =
-          (750 * kTypicalSpeculativeGroupSize) /  max_parallel_resolves;
-    } else if (trial_->group() == max_2s_prefetch) {
-      max_queueing_delay_ms =
-          (2000 * kTypicalSpeculativeGroupSize) /  max_parallel_resolves;
-    }
-
-    TimeDelta max_queueing_delay(
-        TimeDelta::FromMilliseconds(max_queueing_delay_ms));
-
-    DCHECK(!g_predictor);
-    InitNetworkPredictor(max_queueing_delay, max_parallel_resolves, user_prefs,
-                         local_state, preconnect_enabled);
-  }
-}
-
-PredictorInit::~PredictorInit() {
-}
-
-}  // namespace chrome_browser_net