Re-add resource speculative prefetching code

chrome/browser/predictors/resource_prefetch_predictor.cc

Index: chrome/browser/predictors/resource_prefetch_predictor.cc
diff --git a/chrome/browser/predictors/resource_prefetch_predictor.cc b/chrome/browser/predictors/resource_prefetch_predictor.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d0b02a23f78ce0e8ef9c78a3566ea36f35e183f5
--- /dev/null
+++ b/chrome/browser/predictors/resource_prefetch_predictor.cc
@@ -0,0 +1,1222 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/predictors/resource_prefetch_predictor.h"
+
+#include <map>
+#include <set>
+#include <utility>
+
+#include "base/command_line.h"
+#include "base/metrics/histogram.h"
+#include "base/stl_util.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/stringprintf.h"
+#include "base/time/time.h"
+#include "chrome/browser/chrome_notification_types.h"
+#include "chrome/browser/history/history_database.h"
+#include "chrome/browser/history/history_db_task.h"
+#include "chrome/browser/history/history_notifications.h"
+#include "chrome/browser/history/history_service.h"
+#include "chrome/browser/history/history_service_factory.h"
+#include "chrome/browser/predictors/predictor_database.h"
+#include "chrome/browser/predictors/predictor_database_factory.h"
+#include "chrome/browser/predictors/resource_prefetcher_manager.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/common/chrome_switches.h"
+#include "chrome/common/url_constants.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/navigation_controller.h"
+#include "content/public/browser/notification_service.h"
+#include "content/public/browser/notification_source.h"
+#include "content/public/browser/notification_types.h"
+#include "content/public/browser/resource_request_info.h"
+#include "content/public/browser/web_contents.h"
+#include "net/base/mime_util.h"
+#include "net/http/http_response_headers.h"
+#include "net/url_request/url_request.h"
+#include "net/url_request/url_request_context_getter.h"
+
+using content::BrowserThread;
+
+namespace {
+
+// For reporting whether a subresource is handled or not, and for what reasons.
+enum ResourceStatus {
+  RESOURCE_STATUS_HANDLED = 0,
+  RESOURCE_STATUS_NOT_HTTP_PAGE = 1,
+  RESOURCE_STATUS_NOT_HTTP_RESOURCE = 2,
+  RESOURCE_STATUS_UNSUPPORTED_MIME_TYPE = 4,
+  RESOURCE_STATUS_NOT_GET = 8,
+  RESOURCE_STATUS_URL_TOO_LONG = 16,
+  RESOURCE_STATUS_NOT_CACHEABLE = 32,
+  RESOURCE_STATUS_HEADERS_MISSING = 64,
+  RESOURCE_STATUS_MAX = 128,
+};
+
+// For reporting various interesting events that occur during the loading of a
+// single main frame.
+enum NavigationEvent {
+  NAVIGATION_EVENT_REQUEST_STARTED = 0,
+  NAVIGATION_EVENT_REQUEST_REDIRECTED = 1,
+  NAVIGATION_EVENT_REQUEST_REDIRECTED_EMPTY_URL = 2,
+  NAVIGATION_EVENT_REQUEST_EXPIRED = 3,
+  NAVIGATION_EVENT_RESPONSE_STARTED = 4,
+  NAVIGATION_EVENT_ONLOAD = 5,
+  NAVIGATION_EVENT_ONLOAD_EMPTY_URL = 6,
+  NAVIGATION_EVENT_ONLOAD_UNTRACKED_URL = 7,
+  NAVIGATION_EVENT_ONLOAD_TRACKED_URL = 8,
+  NAVIGATION_EVENT_SHOULD_TRACK_URL = 9,
+  NAVIGATION_EVENT_SHOULD_NOT_TRACK_URL = 10,
+  NAVIGATION_EVENT_URL_TABLE_FULL = 11,
+  NAVIGATION_EVENT_HAVE_PREDICTIONS_FOR_URL = 12,
+  NAVIGATION_EVENT_NO_PREDICTIONS_FOR_URL = 13,
+  NAVIGATION_EVENT_MAIN_FRAME_URL_TOO_LONG = 14,
+  NAVIGATION_EVENT_HOST_TOO_LONG = 15,
+  NAVIGATION_EVENT_COUNT = 16,
+};
+
+// For reporting events of interest that are not tied to any navigation.
+enum ReportingEvent {
+  REPORTING_EVENT_ALL_HISTORY_CLEARED = 0,
+  REPORTING_EVENT_PARTIAL_HISTORY_CLEARED = 1,
+  REPORTING_EVENT_COUNT = 2
+};
+
+void RecordNavigationEvent(NavigationEvent event) {
+  UMA_HISTOGRAM_ENUMERATION("ResourcePrefetchPredictor.NavigationEvent",
+                            event,
+                            NAVIGATION_EVENT_COUNT);
+}
+
+}  // namespace
+
+namespace predictors {
+
+////////////////////////////////////////////////////////////////////////////////
+// History lookup task.
+
+// Used to fetch the visit count for a URL from the History database.
+class GetUrlVisitCountTask : public history::HistoryDBTask {
+ public:
+  typedef ResourcePrefetchPredictor::URLRequestSummary URLRequestSummary;
+  typedef base::Callback<void(
+      size_t,   // Visit count.
+      const NavigationID&,
+      const std::vector<URLRequestSummary>&)> VisitInfoCallback;
+
+  GetUrlVisitCountTask(
+      const NavigationID& navigation_id,
+      std::vector<URLRequestSummary>* requests,
+      VisitInfoCallback callback)
+      : visit_count_(0),
+        navigation_id_(navigation_id),
+        requests_(requests),
+        callback_(callback) {
+    DCHECK(requests_.get());
+  }
+
+  virtual bool RunOnDBThread(history::HistoryBackend* backend,
+                             history::HistoryDatabase* db) OVERRIDE {
+    history::URLRow url_row;
+    if (db->GetRowForURL(navigation_id_.main_frame_url, &url_row))
+      visit_count_ = url_row.visit_count();
+    return true;
+  }
+
+  virtual void DoneRunOnMainThread() OVERRIDE {
+    callback_.Run(visit_count_, navigation_id_, *requests_);
+  }
+
+ private:
+  virtual ~GetUrlVisitCountTask() { }
+
+  int visit_count_;
+  NavigationID navigation_id_;
+  scoped_ptr<std::vector<URLRequestSummary> > requests_;
+  VisitInfoCallback callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(GetUrlVisitCountTask);
+};
+
+////////////////////////////////////////////////////////////////////////////////
+// ResourcePrefetchPredictor static functions.
+
+// static
+bool ResourcePrefetchPredictor::ShouldRecordRequest(
+    net::URLRequest* request,
+    content::ResourceType resource_type) {
+  const content::ResourceRequestInfo* request_info =
+      content::ResourceRequestInfo::ForRequest(request);
+  if (!request_info)
+    return false;
+
+  if (!request_info->IsMainFrame())
+    return false;
+
+  return resource_type == content::RESOURCE_TYPE_MAIN_FRAME &&
+      IsHandledMainPage(request);
+}
+
+// static
+bool ResourcePrefetchPredictor::ShouldRecordResponse(
+    net::URLRequest* response) {
+  const content::ResourceRequestInfo* request_info =
+      content::ResourceRequestInfo::ForRequest(response);
+  if (!request_info)
+    return false;
+
+  if (!request_info->IsMainFrame())
+    return false;
+
+  return request_info->GetResourceType() == content::RESOURCE_TYPE_MAIN_FRAME ?
+      IsHandledMainPage(response) : IsHandledSubresource(response);
+}
+
+// static
+bool ResourcePrefetchPredictor::ShouldRecordRedirect(
+    net::URLRequest* response) {
+  const content::ResourceRequestInfo* request_info =
+      content::ResourceRequestInfo::ForRequest(response);
+  if (!request_info)
+    return false;
+
+  if (!request_info->IsMainFrame())
+    return false;
+
+  return request_info->GetResourceType() == content::RESOURCE_TYPE_MAIN_FRAME &&
+      IsHandledMainPage(response);
+}
+
+// static
+bool ResourcePrefetchPredictor::IsHandledMainPage(net::URLRequest* request) {
+  return request->original_url().scheme() == url::kHttpScheme;
+}
+
+// static
+bool ResourcePrefetchPredictor::IsHandledSubresource(
+    net::URLRequest* response) {
+  int resource_status = 0;
+  if (response->first_party_for_cookies().scheme() != url::kHttpScheme)
+    resource_status |= RESOURCE_STATUS_NOT_HTTP_PAGE;
+
+  if (response->original_url().scheme() != url::kHttpScheme)
+    resource_status |= RESOURCE_STATUS_NOT_HTTP_RESOURCE;
+
+  std::string mime_type;
+  response->GetMimeType(&mime_type);
+  if (!mime_type.empty() &&
+      !net::IsSupportedImageMimeType(mime_type.c_str()) &&
+      !net::IsSupportedJavascriptMimeType(mime_type.c_str()) &&
+      !net::MatchesMimeType("text/css", mime_type)) {
+    resource_status |= RESOURCE_STATUS_UNSUPPORTED_MIME_TYPE;
+  }
+
+  if (response->method() != "GET")
+    resource_status |= RESOURCE_STATUS_NOT_GET;
+
+  if (response->original_url().spec().length() >
+      ResourcePrefetchPredictorTables::kMaxStringLength) {
+    resource_status |= RESOURCE_STATUS_URL_TOO_LONG;
+  }
+
+  if (!response->response_info().headers.get())
+    resource_status |= RESOURCE_STATUS_HEADERS_MISSING;
+
+  if (!IsCacheable(response))
+    resource_status |= RESOURCE_STATUS_NOT_CACHEABLE;
+
+  UMA_HISTOGRAM_ENUMERATION("ResourcePrefetchPredictor.ResourceStatus",
+                            resource_status,
+                            RESOURCE_STATUS_MAX);
+
+  return resource_status == 0;
+}
+
+// static
+bool ResourcePrefetchPredictor::IsCacheable(const net::URLRequest* response) {
+  if (response->was_cached())
+    return true;
+
+  // For non cached responses, we will ensure that the freshness lifetime is
+  // some sane value.
+  const net::HttpResponseInfo& response_info = response->response_info();
+  if (!response_info.headers.get())
+    return false;
+  base::Time response_time(response_info.response_time);
+  response_time += base::TimeDelta::FromSeconds(1);
+  base::TimeDelta freshness = response_info.headers->GetFreshnessLifetime(
+      response_time);
+  return freshness > base::TimeDelta();
+}
+
+// static
+content::ResourceType ResourcePrefetchPredictor::GetResourceTypeFromMimeType(
+    const std::string& mime_type,
+    content::ResourceType fallback) {
+  if (net::IsSupportedImageMimeType(mime_type.c_str()))
+    return content::RESOURCE_TYPE_IMAGE;
+  else if (net::IsSupportedJavascriptMimeType(mime_type.c_str()))
+    return content::RESOURCE_TYPE_SCRIPT;
+  else if (net::MatchesMimeType("text/css", mime_type))
+    return content::RESOURCE_TYPE_STYLESHEET;
+  else
+    return fallback;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// ResourcePrefetchPredictor structs.
+
+ResourcePrefetchPredictor::URLRequestSummary::URLRequestSummary()
+    : resource_type(content::RESOURCE_TYPE_LAST_TYPE),
+      was_cached(false) {
+}
+
+ResourcePrefetchPredictor::URLRequestSummary::URLRequestSummary(
+    const URLRequestSummary& other)
+        : navigation_id(other.navigation_id),
+          resource_url(other.resource_url),
+          resource_type(other.resource_type),
+          mime_type(other.mime_type),
+          was_cached(other.was_cached),
+          redirect_url(other.redirect_url) {
+}
+
+ResourcePrefetchPredictor::URLRequestSummary::~URLRequestSummary() {
+}
+
+ResourcePrefetchPredictor::Result::Result(
+    PrefetchKeyType i_key_type,
+    ResourcePrefetcher::RequestVector* i_requests)
+    : key_type(i_key_type),
+      requests(i_requests) {
+}
+
+ResourcePrefetchPredictor::Result::~Result() {
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// ResourcePrefetchPredictor.
+
+ResourcePrefetchPredictor::ResourcePrefetchPredictor(
+    const ResourcePrefetchPredictorConfig& config,
+    Profile* profile)
+    : profile_(profile),
+      config_(config),
+      initialization_state_(NOT_INITIALIZED),
+      tables_(PredictorDatabaseFactory::GetForProfile(
+          profile)->resource_prefetch_tables()),
+      results_map_deleter_(&results_map_) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  // Some form of learning has to be enabled.
+  DCHECK(config_.IsLearningEnabled());
+  if (config_.IsURLPrefetchingEnabled())
+    DCHECK(config_.IsURLLearningEnabled());
+  if (config_.IsHostPrefetchingEnabled())
+    DCHECK(config_.IsHostLearningEnabled());
+}
+
+ResourcePrefetchPredictor::~ResourcePrefetchPredictor() {
+}
+
+void ResourcePrefetchPredictor::RecordURLRequest(
+    const URLRequestSummary& request) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  if (initialization_state_ != INITIALIZED)
+    return;
+
+  CHECK_EQ(request.resource_type, content::RESOURCE_TYPE_MAIN_FRAME);
+  OnMainFrameRequest(request);
+}
+
+void ResourcePrefetchPredictor::RecordURLResponse(
+    const URLRequestSummary& response) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  if (initialization_state_ != INITIALIZED)
+    return;
+
+  if (response.resource_type == content::RESOURCE_TYPE_MAIN_FRAME)
+    OnMainFrameResponse(response);
+  else
+    OnSubresourceResponse(response);
+}
+
+void ResourcePrefetchPredictor::RecordURLRedirect(
+    const URLRequestSummary& response) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  if (initialization_state_ != INITIALIZED)
+    return;
+
+  CHECK_EQ(response.resource_type, content::RESOURCE_TYPE_MAIN_FRAME);
+  OnMainFrameRedirect(response);
+}
+
+void ResourcePrefetchPredictor::RecordMainFrameLoadComplete(
+    const NavigationID& navigation_id) {
+  switch (initialization_state_) {
+    case NOT_INITIALIZED:
+      StartInitialization();
+      break;
+    case INITIALIZING:
+      break;
+    case INITIALIZED: {
+      RecordNavigationEvent(NAVIGATION_EVENT_ONLOAD);
+      // WebContents can return an empty URL if the navigation entry
+      // corresponding to the navigation has not been created yet.
+      if (navigation_id.main_frame_url.is_empty())
+        RecordNavigationEvent(NAVIGATION_EVENT_ONLOAD_EMPTY_URL);
+      else
+        OnNavigationComplete(navigation_id);
+      break;
+    }
+    default:
+      NOTREACHED() << "Unexpected initialization_state_: "
+                   << initialization_state_;
+  }
+}
+
+void ResourcePrefetchPredictor::FinishedPrefetchForNavigation(
+    const NavigationID& navigation_id,
+    PrefetchKeyType key_type,
+    ResourcePrefetcher::RequestVector* requests) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  Result* result = new Result(key_type, requests);
+  // Add the results to the results map.
+  if (!results_map_.insert(std::make_pair(navigation_id, result)).second) {
+    DLOG(FATAL) << "Returning results for existing navigation.";
+    delete result;
+  }
+}
+
+void ResourcePrefetchPredictor::Observe(
+    int type,
+    const content::NotificationSource& source,
+    const content::NotificationDetails& details) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  switch (type) {
+    case chrome::NOTIFICATION_HISTORY_LOADED: {
+      DCHECK_EQ(initialization_state_, INITIALIZING);
+      notification_registrar_.Remove(this,
+                                     chrome::NOTIFICATION_HISTORY_LOADED,
+                                     content::Source<Profile>(profile_));
+      OnHistoryAndCacheLoaded();
+      break;
+    }
+
+    case chrome::NOTIFICATION_HISTORY_URLS_DELETED: {
+      DCHECK_EQ(initialization_state_, INITIALIZED);
+      const content::Details<const history::URLsDeletedDetails>
+          urls_deleted_details =
+              content::Details<const history::URLsDeletedDetails>(details);
+      if (urls_deleted_details->all_history) {
+        DeleteAllUrls();
+        UMA_HISTOGRAM_ENUMERATION("ResourcePrefetchPredictor.ReportingEvent",
+                                  REPORTING_EVENT_ALL_HISTORY_CLEARED,
+                                  REPORTING_EVENT_COUNT);
+      } else {
+        DeleteUrls(urls_deleted_details->rows);
+        UMA_HISTOGRAM_ENUMERATION("ResourcePrefetchPredictor.ReportingEvent",
+                                  REPORTING_EVENT_PARTIAL_HISTORY_CLEARED,
+                                  REPORTING_EVENT_COUNT);
+      }
+      break;
+    }
+
+    default:
+      NOTREACHED() << "Unexpected notification observed.";
+      break;
+  }
+}
+
+void ResourcePrefetchPredictor::Shutdown() {
+  if (prefetch_manager_.get()) {
+    prefetch_manager_->ShutdownOnUIThread();
+    prefetch_manager_ = NULL;
+  }
+}
+
+void ResourcePrefetchPredictor::OnMainFrameRequest(
+    const URLRequestSummary& request) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  DCHECK_EQ(INITIALIZED, initialization_state_);
+
+  RecordNavigationEvent(NAVIGATION_EVENT_REQUEST_STARTED);
+
+  StartPrefetching(request.navigation_id);
+
+  // Cleanup older navigations.
+  CleanupAbandonedNavigations(request.navigation_id);
+
+  // New empty navigation entry.
+  inflight_navigations_.insert(std::make_pair(
+      request.navigation_id,
+      make_linked_ptr(new std::vector<URLRequestSummary>())));
+}
+
+void ResourcePrefetchPredictor::OnMainFrameResponse(
+    const URLRequestSummary& response) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  if (initialization_state_ != INITIALIZED)
+    return;
+
+  RecordNavigationEvent(NAVIGATION_EVENT_RESPONSE_STARTED);
+
+  StopPrefetching(response.navigation_id);
+}
+
+void ResourcePrefetchPredictor::OnMainFrameRedirect(
+    const URLRequestSummary& response) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  RecordNavigationEvent(NAVIGATION_EVENT_REQUEST_REDIRECTED);
+
+  // TODO(shishir): There are significant gains to be had here if we can use the
+  // start URL in a redirect chain as the key to start prefetching. We can save
+  // of redirect times considerably assuming that the redirect chains do not
+  // change.
+
+  // Stop any inflight prefetching. Remove the older navigation.
+  StopPrefetching(response.navigation_id);
+  inflight_navigations_.erase(response.navigation_id);
+
+  // A redirect will not lead to another OnMainFrameRequest call, so record the
+  // redirect url as a new navigation.
+
+  // The redirect url may be empty if the url was invalid.
+  if (response.redirect_url.is_empty()) {
+    RecordNavigationEvent(NAVIGATION_EVENT_REQUEST_REDIRECTED_EMPTY_URL);
+    return;
+  }
+
+  NavigationID navigation_id(response.navigation_id);
+  navigation_id.main_frame_url = response.redirect_url;
+  inflight_navigations_.insert(std::make_pair(
+      navigation_id,
+      make_linked_ptr(new std::vector<URLRequestSummary>())));
+}
+
+void ResourcePrefetchPredictor::OnSubresourceResponse(
+    const URLRequestSummary& response) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  NavigationMap::const_iterator nav_it =
+        inflight_navigations_.find(response.navigation_id);
+  if (nav_it == inflight_navigations_.end()) {
+    return;
+  }
+
+  nav_it->second->push_back(response);
+}
+
+void ResourcePrefetchPredictor::OnNavigationComplete(
+    const NavigationID& navigation_id) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  NavigationMap::iterator nav_it =
+      inflight_navigations_.find(navigation_id);
+  if (nav_it == inflight_navigations_.end()) {
+    RecordNavigationEvent(NAVIGATION_EVENT_ONLOAD_UNTRACKED_URL);
+    return;
+  }
+  RecordNavigationEvent(NAVIGATION_EVENT_ONLOAD_TRACKED_URL);
+
+  // Report any stats.
+  if (prefetch_manager_.get()) {
+    ResultsMap::iterator results_it = results_map_.find(navigation_id);
+    bool have_prefetch_results = results_it != results_map_.end();
+    UMA_HISTOGRAM_BOOLEAN("ResourcePrefetchPredictor.HavePrefetchResults",
+                          have_prefetch_results);
+    if (have_prefetch_results) {
+      ReportAccuracyStats(results_it->second->key_type,
+                          *(nav_it->second),
+                          results_it->second->requests.get());
+    }
+  } else {
+    scoped_ptr<ResourcePrefetcher::RequestVector> requests(
+        new ResourcePrefetcher::RequestVector);
+    PrefetchKeyType key_type;
+    if (GetPrefetchData(navigation_id, requests.get(), &key_type)) {
+      RecordNavigationEvent(NAVIGATION_EVENT_HAVE_PREDICTIONS_FOR_URL);
+      ReportPredictedAccuracyStats(key_type,
+                                   *(nav_it->second),
+                                   *requests);
+    } else {
+      RecordNavigationEvent(NAVIGATION_EVENT_NO_PREDICTIONS_FOR_URL);
+    }
+  }
+
+  // Remove the navigation from the inflight navigations.
+  std::vector<URLRequestSummary>* requests = (nav_it->second).release();
+  inflight_navigations_.erase(nav_it);
+
+  // Kick off history lookup to determine if we should record the URL.
+  HistoryService* history_service = HistoryServiceFactory::GetForProfile(
+      profile_, Profile::EXPLICIT_ACCESS);
+  DCHECK(history_service);
+  history_service->ScheduleDBTask(
+      scoped_ptr<history::HistoryDBTask>(
+          new GetUrlVisitCountTask(
+              navigation_id,
+              requests,
+              base::Bind(&ResourcePrefetchPredictor::OnVisitCountLookup,
+                         AsWeakPtr()))),
+      &history_lookup_consumer_);
+}
+
+bool ResourcePrefetchPredictor::GetPrefetchData(
+    const NavigationID& navigation_id,
+    ResourcePrefetcher::RequestVector* prefetch_requests,
+    PrefetchKeyType* key_type) {
+  DCHECK(prefetch_requests);
+  DCHECK(key_type);
+
+  *key_type = PREFETCH_KEY_TYPE_URL;
+  const GURL& main_frame_url = navigation_id.main_frame_url;
+
+  bool use_url_data = config_.IsPrefetchingEnabled() ?
+      config_.IsURLPrefetchingEnabled() : config_.IsURLLearningEnabled();
+  if (use_url_data) {
+    PrefetchDataMap::const_iterator iterator =
+        url_table_cache_->find(main_frame_url.spec());
+    if (iterator != url_table_cache_->end())
+      PopulatePrefetcherRequest(iterator->second, prefetch_requests);
+  }
+  if (!prefetch_requests->empty())
+    return true;
+
+  bool use_host_data = config_.IsPrefetchingEnabled() ?
+      config_.IsHostPrefetchingEnabled() : config_.IsHostLearningEnabled();
+  if (use_host_data) {
+    PrefetchDataMap::const_iterator iterator =
+        host_table_cache_->find(main_frame_url.host());
+    if (iterator != host_table_cache_->end()) {
+      *key_type = PREFETCH_KEY_TYPE_HOST;
+      PopulatePrefetcherRequest(iterator->second, prefetch_requests);
+    }
+  }
+
+  return !prefetch_requests->empty();
+}
+
+void ResourcePrefetchPredictor::PopulatePrefetcherRequest(
+    const PrefetchData& data,
+    ResourcePrefetcher::RequestVector* requests) {
+  for (ResourceRows::const_iterator it = data.resources.begin();
+       it != data.resources.end(); ++it) {
+    float confidence = static_cast<float>(it->number_of_hits) /
+        (it->number_of_hits + it->number_of_misses);
+    if (confidence < config_.min_resource_confidence_to_trigger_prefetch ||
+        it->number_of_hits < config_.min_resource_hits_to_trigger_prefetch) {
+      continue;
+    }
+
+    ResourcePrefetcher::Request* req = new ResourcePrefetcher::Request(
+        it->resource_url);
+    requests->push_back(req);
+  }
+}
+
+void ResourcePrefetchPredictor::StartPrefetching(
+    const NavigationID& navigation_id) {
+  if (!prefetch_manager_.get())  // Prefetching not enabled.
+    return;
+
+  // Prefer URL based data first.
+  scoped_ptr<ResourcePrefetcher::RequestVector> requests(
+      new ResourcePrefetcher::RequestVector);
+  PrefetchKeyType key_type;
+  if (!GetPrefetchData(navigation_id, requests.get(), &key_type)) {
+    // No prefetching data at host or URL level.
+    return;
+  }
+
+  BrowserThread::PostTask(BrowserThread::IO, FROM_HERE,
+      base::Bind(&ResourcePrefetcherManager::MaybeAddPrefetch,
+                 prefetch_manager_,
+                 navigation_id,
+                 key_type,
+                 base::Passed(&requests)));
+}
+
+void ResourcePrefetchPredictor::StopPrefetching(
+    const NavigationID& navigation_id) {
+  if (!prefetch_manager_.get())  // Not enabled.
+    return;
+
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      base::Bind(&ResourcePrefetcherManager::MaybeRemovePrefetch,
+                 prefetch_manager_,
+                 navigation_id));
+}
+
+void ResourcePrefetchPredictor::StartInitialization() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  DCHECK_EQ(initialization_state_, NOT_INITIALIZED);
+  initialization_state_ = INITIALIZING;
+
+  // Create local caches using the database as loaded.
+  scoped_ptr<PrefetchDataMap> url_data_map(new PrefetchDataMap());
+  scoped_ptr<PrefetchDataMap> host_data_map(new PrefetchDataMap());
+  PrefetchDataMap* url_data_ptr = url_data_map.get();
+  PrefetchDataMap* host_data_ptr = host_data_map.get();
+
+  BrowserThread::PostTaskAndReply(
+      BrowserThread::DB, FROM_HERE,
+      base::Bind(&ResourcePrefetchPredictorTables::GetAllData,
+                 tables_, url_data_ptr, host_data_ptr),
+      base::Bind(&ResourcePrefetchPredictor::CreateCaches, AsWeakPtr(),
+                 base::Passed(&url_data_map), base::Passed(&host_data_map)));
+}
+
+void ResourcePrefetchPredictor::CreateCaches(
+    scoped_ptr<PrefetchDataMap> url_data_map,
+    scoped_ptr<PrefetchDataMap> host_data_map) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  DCHECK_EQ(initialization_state_, INITIALIZING);
+  DCHECK(!url_table_cache_);
+  DCHECK(!host_table_cache_);
+  DCHECK(inflight_navigations_.empty());
+
+  url_table_cache_.reset(url_data_map.release());
+  host_table_cache_.reset(host_data_map.release());
+
+  UMA_HISTOGRAM_COUNTS("ResourcePrefetchPredictor.UrlTableMainFrameUrlCount",
+                       url_table_cache_->size());
+  UMA_HISTOGRAM_COUNTS("ResourcePrefetchPredictor.HostTableHostCount",
+                       host_table_cache_->size());
+
+  // Add notifications for history loading if it is not ready.
+  HistoryService* history_service = HistoryServiceFactory::GetForProfile(
+    profile_, Profile::EXPLICIT_ACCESS);
+  if (!history_service) {
+    notification_registrar_.Add(this, chrome::NOTIFICATION_HISTORY_LOADED,
+                                content::Source<Profile>(profile_));
+  } else {
+    OnHistoryAndCacheLoaded();
+  }
+}
+
+void ResourcePrefetchPredictor::OnHistoryAndCacheLoaded() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  DCHECK_EQ(initialization_state_, INITIALIZING);
+
+  notification_registrar_.Add(this,
+                              chrome::NOTIFICATION_HISTORY_URLS_DELETED,
+                              content::Source<Profile>(profile_));
+
+  // Initialize the prefetch manager only if prefetching is enabled.
+  if (config_.IsPrefetchingEnabled()) {
+    prefetch_manager_ = new ResourcePrefetcherManager(
+        this, config_, profile_->GetRequestContext());
+  }
+
+  initialization_state_ = INITIALIZED;
+}
+
+void ResourcePrefetchPredictor::CleanupAbandonedNavigations(
+    const NavigationID& navigation_id) {
+  static const base::TimeDelta max_navigation_age =
+      base::TimeDelta::FromSeconds(config_.max_navigation_lifetime_seconds);
+
+  base::TimeTicks time_now = base::TimeTicks::Now();
+  for (NavigationMap::iterator it = inflight_navigations_.begin();
+       it != inflight_navigations_.end();) {
+    if (it->first.IsSameRenderer(navigation_id) ||
+        (time_now - it->first.creation_time > max_navigation_age)) {
+      inflight_navigations_.erase(it++);
+      RecordNavigationEvent(NAVIGATION_EVENT_REQUEST_EXPIRED);
+    } else {
+      ++it;
+    }
+  }
+  for (ResultsMap::iterator it = results_map_.begin();
+       it != results_map_.end();) {
+    if (it->first.IsSameRenderer(navigation_id) ||
+        (time_now - it->first.creation_time > max_navigation_age)) {
+      delete it->second;
+      results_map_.erase(it++);
+    } else {
+      ++it;
+    }
+  }
+}
+
+void ResourcePrefetchPredictor::DeleteAllUrls() {
+  inflight_navigations_.clear();
+  url_table_cache_->clear();
+  host_table_cache_->clear();
+
+  BrowserThread::PostTask(BrowserThread::DB, FROM_HERE,
+      base::Bind(&ResourcePrefetchPredictorTables::DeleteAllData, tables_));
+}
+
+void ResourcePrefetchPredictor::DeleteUrls(const history::URLRows& urls) {
+  // Check all the urls in the database and pick out the ones that are present
+  // in the cache.
+  std::vector<std::string> urls_to_delete, hosts_to_delete;
+
+  for (history::URLRows::const_iterator it = urls.begin(); it != urls.end();
+       ++it) {
+    const std::string url_spec = it->url().spec();
+    if (url_table_cache_->find(url_spec) != url_table_cache_->end()) {
+      urls_to_delete.push_back(url_spec);
+      url_table_cache_->erase(url_spec);
+    }
+
+    const std::string host = it->url().host();
+    if (host_table_cache_->find(host) != host_table_cache_->end()) {
+      hosts_to_delete.push_back(host);
+      host_table_cache_->erase(host);
+    }
+  }
+
+  if (!urls_to_delete.empty() || !hosts_to_delete.empty()) {
+    BrowserThread::PostTask(BrowserThread::DB, FROM_HERE,
+        base::Bind(&ResourcePrefetchPredictorTables::DeleteData,
+                   tables_,
+                   urls_to_delete,
+                   hosts_to_delete));
+  }
+}
+
+void ResourcePrefetchPredictor::RemoveOldestEntryInPrefetchDataMap(
+    PrefetchKeyType key_type,
+    PrefetchDataMap* data_map) {
+  if (data_map->empty())
+    return;
+
+  base::Time oldest_time;
+  std::string key_to_delete;
+  for (PrefetchDataMap::iterator it = data_map->begin();
+       it != data_map->end(); ++it) {
+    if (key_to_delete.empty() || it->second.last_visit < oldest_time) {
+      key_to_delete = it->first;
+      oldest_time = it->second.last_visit;
+    }
+  }
+
+  data_map->erase(key_to_delete);
+    BrowserThread::PostTask(BrowserThread::DB, FROM_HERE,
+        base::Bind(&ResourcePrefetchPredictorTables::DeleteSingleDataPoint,
+                   tables_,
+                   key_to_delete,
+                   key_type));
+}
+
+void ResourcePrefetchPredictor::OnVisitCountLookup(
+    size_t visit_count,
+    const NavigationID& navigation_id,
+    const std::vector<URLRequestSummary>& requests) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  UMA_HISTOGRAM_COUNTS("ResourcePrefetchPredictor.HistoryVisitCountForUrl",
+                       visit_count);
+
+  // URL level data - merge only if we are already saving the data, or we it
+  // meets the cutoff requirement.
+  const std::string url_spec = navigation_id.main_frame_url.spec();
+  bool already_tracking = url_table_cache_->find(url_spec) !=
+      url_table_cache_->end();
+  bool should_track_url = already_tracking ||
+      (visit_count >= config_.min_url_visit_count);
+
+  if (should_track_url) {
+    RecordNavigationEvent(NAVIGATION_EVENT_SHOULD_TRACK_URL);
+
+    if (config_.IsURLLearningEnabled()) {
+      LearnNavigation(url_spec, PREFETCH_KEY_TYPE_URL, requests,
+                      config_.max_urls_to_track, url_table_cache_.get());
+    }
+  } else {
+    RecordNavigationEvent(NAVIGATION_EVENT_SHOULD_NOT_TRACK_URL);
+  }
+
+  // Host level data - no cutoff, always learn the navigation if enabled.
+  if (config_.IsHostLearningEnabled()) {
+    LearnNavigation(navigation_id.main_frame_url.host(),
+                    PREFETCH_KEY_TYPE_HOST,
+                    requests,
+                    config_.max_hosts_to_track,
+                    host_table_cache_.get());
+  }
+
+  // Remove the navigation from the results map.
+  ResultsMap::iterator results_it = results_map_.find(navigation_id);
+  if (results_it != results_map_.end()) {
+    delete results_it->second;
+    results_map_.erase(results_it);
+  }
+}
+
+void ResourcePrefetchPredictor::LearnNavigation(
+    const std::string& key,
+    PrefetchKeyType key_type,
+    const std::vector<URLRequestSummary>& new_resources,
+    size_t max_data_map_size,
+    PrefetchDataMap* data_map) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  // If the primary key is too long reject it.
+  if (key.length() > ResourcePrefetchPredictorTables::kMaxStringLength) {
+    if (key_type == PREFETCH_KEY_TYPE_HOST)
+      RecordNavigationEvent(NAVIGATION_EVENT_HOST_TOO_LONG);
+    else
+      RecordNavigationEvent(NAVIGATION_EVENT_MAIN_FRAME_URL_TOO_LONG);
+    return;
+  }
+
+  PrefetchDataMap::iterator cache_entry = data_map->find(key);
+  if (cache_entry == data_map->end()) {
+    if (data_map->size() >= max_data_map_size) {
+      // The table is full, delete an entry.
+      RemoveOldestEntryInPrefetchDataMap(key_type, data_map);
+    }
+
+    cache_entry = data_map->insert(std::make_pair(
+        key, PrefetchData(key_type, key))).first;
+    cache_entry->second.last_visit = base::Time::Now();
+    size_t new_resources_size = new_resources.size();
+    std::set<GURL> resources_seen;
+    for (size_t i = 0; i < new_resources_size; ++i) {
+      if (resources_seen.find(new_resources[i].resource_url) !=
+          resources_seen.end()) {
+        continue;
+      }
+      ResourceRow row_to_add;
+      row_to_add.resource_url = new_resources[i].resource_url;
+      row_to_add.resource_type = new_resources[i].resource_type;
+      row_to_add.number_of_hits = 1;
+      row_to_add.average_position = i + 1;
+      cache_entry->second.resources.push_back(row_to_add);
+      resources_seen.insert(new_resources[i].resource_url);
+    }
+  } else {
+    ResourceRows& old_resources = cache_entry->second.resources;
+    cache_entry->second.last_visit = base::Time::Now();
+
+    // Build indices over the data.
+    std::map<GURL, int> new_index, old_index;
+    int new_resources_size = static_cast<int>(new_resources.size());
+    for (int i = 0; i < new_resources_size; ++i) {
+      const URLRequestSummary& summary = new_resources[i];
+      // Take the first occurence of every url.
+      if (new_index.find(summary.resource_url) == new_index.end())
+        new_index[summary.resource_url] = i;
+    }
+    int old_resources_size = static_cast<int>(old_resources.size());
+    for (int i = 0; i < old_resources_size; ++i) {
+      const ResourceRow& row = old_resources[i];
+      DCHECK(old_index.find(row.resource_url) == old_index.end());
+      old_index[row.resource_url] = i;
+    }
+
+    // Go through the old urls and update their hit/miss counts.
+    for (int i = 0; i < old_resources_size; ++i) {
+      ResourceRow& old_row = old_resources[i];
+      if (new_index.find(old_row.resource_url) == new_index.end()) {
+        ++old_row.number_of_misses;
+        ++old_row.consecutive_misses;
+      } else {
+        const URLRequestSummary& new_row =
+            new_resources[new_index[old_row.resource_url]];
+
+        // Update the resource type since it could have changed.
+        if (new_row.resource_type != content::RESOURCE_TYPE_LAST_TYPE)
+          old_row.resource_type = new_row.resource_type;
+
+        int position = new_index[old_row.resource_url] + 1;
+        int total = old_row.number_of_hits + old_row.number_of_misses;
+        old_row.average_position =
+            ((old_row.average_position * total) + position) / (total + 1);
+        ++old_row.number_of_hits;
+        old_row.consecutive_misses = 0;
+      }
+    }
+
+    // Add the new ones that we have not seen before.
+    for (int i = 0; i < new_resources_size; ++i) {
+      const URLRequestSummary& summary = new_resources[i];
+      if (old_index.find(summary.resource_url) != old_index.end())
+        continue;
+
+      // Only need to add new stuff.
+      ResourceRow row_to_add;
+      row_to_add.resource_url = summary.resource_url;
+      row_to_add.resource_type = summary.resource_type;
+      row_to_add.number_of_hits = 1;
+      row_to_add.average_position = i + 1;
+      old_resources.push_back(row_to_add);
+
+      // To ensure we dont add the same url twice.
+      old_index[summary.resource_url] = 0;
+    }
+  }
+
+  // Trim and sort the resources after the update.
+  ResourceRows& resources = cache_entry->second.resources;
+  for (ResourceRows::iterator it = resources.begin();
+       it != resources.end();) {
+    it->UpdateScore();
+    if (it->consecutive_misses >= config_.max_consecutive_misses)
+      it = resources.erase(it);
+    else
+      ++it;
+  }
+  std::sort(resources.begin(), resources.end(),
+            ResourcePrefetchPredictorTables::ResourceRowSorter());
+  if (resources.size() > config_.max_resources_per_entry)
+    resources.resize(config_.max_resources_per_entry);
+
+  // If the row has no resources, remove it from the cache and delete the
+  // entry in the database. Else update the database.
+  if (resources.empty()) {
+    data_map->erase(key);
+    BrowserThread::PostTask(
+        BrowserThread::DB, FROM_HERE,
+        base::Bind(&ResourcePrefetchPredictorTables::DeleteSingleDataPoint,
+                   tables_,
+                   key,
+                   key_type));
+  } else {
+    bool is_host = key_type == PREFETCH_KEY_TYPE_HOST;
+    PrefetchData empty_data(
+        !is_host ? PREFETCH_KEY_TYPE_HOST : PREFETCH_KEY_TYPE_URL,
+        std::string());
+    const PrefetchData& host_data = is_host ? cache_entry->second : empty_data;
+    const PrefetchData& url_data = is_host ? empty_data : cache_entry->second;
+    BrowserThread::PostTask(
+        BrowserThread::DB, FROM_HERE,
+        base::Bind(&ResourcePrefetchPredictorTables::UpdateData,
+                   tables_,
+                   url_data,
+                   host_data));
+  }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Accuracy measurement.
+
+void ResourcePrefetchPredictor::ReportAccuracyStats(
+    PrefetchKeyType key_type,
+    const std::vector<URLRequestSummary>& actual,
+    ResourcePrefetcher::RequestVector* prefetched) const {
+  // Annotate the results.
+  std::map<GURL, bool> actual_resources;
+  for (std::vector<URLRequestSummary>::const_iterator it = actual.begin();
+       it != actual.end(); ++it) {
+    actual_resources[it->resource_url] = it->was_cached;
+  }
+
+  int prefetch_cancelled = 0, prefetch_failed = 0, prefetch_not_started = 0;
+  // 'a_' -> actual, 'p_' -> predicted.
+  int p_cache_a_cache = 0, p_cache_a_network = 0, p_cache_a_notused = 0,
+      p_network_a_cache = 0, p_network_a_network = 0, p_network_a_notused = 0;
+
+  for (ResourcePrefetcher::RequestVector::iterator it = prefetched->begin();
+       it != prefetched->end(); ++it) {
+    ResourcePrefetcher::Request* req = *it;
+
+    // Set the usage states if the resource was actually used.
+    std::map<GURL, bool>::iterator actual_it = actual_resources.find(
+        req->resource_url);
+    if (actual_it != actual_resources.end()) {
+      if (actual_it->second) {
+        req->usage_status =
+            ResourcePrefetcher::Request::USAGE_STATUS_FROM_CACHE;
+      } else {
+        req->usage_status =
+            ResourcePrefetcher::Request::USAGE_STATUS_FROM_NETWORK;
+      }
+    }
+
+    switch (req->prefetch_status) {
+      // TODO(shishir): Add histogram for each cancellation reason.
+      case ResourcePrefetcher::Request::PREFETCH_STATUS_REDIRECTED:
+      case ResourcePrefetcher::Request::PREFETCH_STATUS_AUTH_REQUIRED:
+      case ResourcePrefetcher::Request::PREFETCH_STATUS_CERT_REQUIRED:
+      case ResourcePrefetcher::Request::PREFETCH_STATUS_CERT_ERROR:
+      case ResourcePrefetcher::Request::PREFETCH_STATUS_CANCELLED:
+        ++prefetch_cancelled;
+        break;
+
+      case ResourcePrefetcher::Request::PREFETCH_STATUS_FAILED:
+        ++prefetch_failed;
+        break;
+
+      case ResourcePrefetcher::Request::PREFETCH_STATUS_FROM_CACHE:
+        if (req->usage_status ==
+            ResourcePrefetcher::Request::USAGE_STATUS_FROM_CACHE)
+          ++p_cache_a_cache;
+        else if (req->usage_status ==
+                 ResourcePrefetcher::Request::USAGE_STATUS_FROM_NETWORK)
+          ++p_cache_a_network;
+        else
+          ++p_cache_a_notused;
+        break;
+
+      case ResourcePrefetcher::Request::PREFETCH_STATUS_FROM_NETWORK:
+          if (req->usage_status ==
+              ResourcePrefetcher::Request::USAGE_STATUS_FROM_CACHE)
+            ++p_network_a_cache;
+          else if (req->usage_status ==
+                   ResourcePrefetcher::Request::USAGE_STATUS_FROM_NETWORK)
+            ++p_network_a_network;
+          else
+            ++p_network_a_notused;
+        break;
+
+      case ResourcePrefetcher::Request::PREFETCH_STATUS_NOT_STARTED:
+        ++prefetch_not_started;
+        break;
+
+      case ResourcePrefetcher::Request::PREFETCH_STATUS_STARTED:
+        DLOG(FATAL) << "Invalid prefetch status";
+        break;
+    }
+  }
+
+  int total_prefetched = p_cache_a_cache + p_cache_a_network + p_cache_a_notused
+      + p_network_a_cache + p_network_a_network + p_network_a_notused;
+
+  std::string histogram_type = key_type == PREFETCH_KEY_TYPE_HOST ? "Host." :
+      "Url.";
+
+  // Macros to avoid using the STATIC_HISTOGRAM_POINTER_BLOCK in UMA_HISTOGRAM
+  // definitions.
+#define RPP_HISTOGRAM_PERCENTAGE(suffix, value) \
+  { \
+    std::string name = "ResourcePrefetchPredictor." + histogram_type + suffix; \
+    std::string g_name = "ResourcePrefetchPredictor." + std::string(suffix); \
+    base::HistogramBase* histogram = base::LinearHistogram::FactoryGet( \
+        name, 1, 101, 102, base::Histogram::kUmaTargetedHistogramFlag); \
+    histogram->Add(value); \
+    UMA_HISTOGRAM_PERCENTAGE(g_name, value); \
+  }
+
+  RPP_HISTOGRAM_PERCENTAGE("PrefetchCancelled",
+                           prefetch_cancelled * 100.0 / total_prefetched);
+  RPP_HISTOGRAM_PERCENTAGE("PrefetchFailed",
+                           prefetch_failed * 100.0 / total_prefetched);
+  RPP_HISTOGRAM_PERCENTAGE("PrefetchFromCacheUsedFromCache",
+                           p_cache_a_cache * 100.0 / total_prefetched);
+  RPP_HISTOGRAM_PERCENTAGE("PrefetchFromCacheUsedFromNetwork",
+                           p_cache_a_network * 100.0 / total_prefetched);
+  RPP_HISTOGRAM_PERCENTAGE("PrefetchFromCacheNotUsed",
+                           p_cache_a_notused * 100.0 / total_prefetched);
+  RPP_HISTOGRAM_PERCENTAGE("PrefetchFromNetworkUsedFromCache",
+                           p_network_a_cache * 100.0 / total_prefetched);
+  RPP_HISTOGRAM_PERCENTAGE("PrefetchFromNetworkUsedFromNetwork",
+                           p_network_a_network * 100.0 / total_prefetched);
+  RPP_HISTOGRAM_PERCENTAGE("PrefetchFromNetworkNotUsed",
+                           p_network_a_notused * 100.0 / total_prefetched);
+
+  RPP_HISTOGRAM_PERCENTAGE(
+      "PrefetchNotStarted",
+      prefetch_not_started * 100.0 / (prefetch_not_started + total_prefetched));
+
+#undef RPP_HISTOGRAM_PERCENTAGE
+}
+
+void ResourcePrefetchPredictor::ReportPredictedAccuracyStats(
+    PrefetchKeyType key_type,
+    const std::vector<URLRequestSummary>& actual,
+    const ResourcePrefetcher::RequestVector& predicted) const {
+  std::map<GURL, bool> actual_resources;
+  int from_network = 0;
+  for (std::vector<URLRequestSummary>::const_iterator it = actual.begin();
+       it != actual.end(); ++it) {
+    actual_resources[it->resource_url] = it->was_cached;
+    if (!it->was_cached)
+      ++from_network;
+  }
+
+  // Measure the accuracy at 25, 50 predicted resources.
+  ReportPredictedAccuracyStatsHelper(key_type, predicted, actual_resources,
+                                     from_network, 25);
+  ReportPredictedAccuracyStatsHelper(key_type, predicted, actual_resources,
+                                     from_network, 50);
+}
+
+void ResourcePrefetchPredictor::ReportPredictedAccuracyStatsHelper(
+    PrefetchKeyType key_type,
+    const ResourcePrefetcher::RequestVector& predicted,
+    const std::map<GURL, bool>& actual,
+    size_t total_resources_fetched_from_network,
+    size_t max_assumed_prefetched) const {
+  int prefetch_cached = 0, prefetch_network = 0, prefetch_missed = 0;
+  int num_assumed_prefetched = std::min(predicted.size(),
+                                        max_assumed_prefetched);
+  if (num_assumed_prefetched == 0)
+    return;
+
+  for (int i = 0; i < num_assumed_prefetched; ++i) {
+    const ResourcePrefetcher::Request& row = *(predicted[i]);
+    std::map<GURL, bool>::const_iterator it = actual.find(row.resource_url);
+    if (it == actual.end()) {
+      ++prefetch_missed;
+    } else if (it->second) {
+      ++prefetch_cached;
+    } else {
+      ++prefetch_network;
+    }
+  }
+
+  std::string prefix = key_type == PREFETCH_KEY_TYPE_HOST ?
+      "ResourcePrefetchPredictor.Host.Predicted" :
+      "ResourcePrefetchPredictor.Url.Predicted";
+  std::string suffix = "_" + base::IntToString(max_assumed_prefetched);
+
+  // Macros to avoid using the STATIC_HISTOGRAM_POINTER_BLOCK in UMA_HISTOGRAM
+  // definitions.
+#define RPP_PREDICTED_HISTOGRAM_COUNTS(name, value) \
+  { \
+    std::string full_name = prefix + name + suffix; \
+    base::HistogramBase* histogram = base::Histogram::FactoryGet( \
+        full_name, 1, 1000000, 50, \
+        base::Histogram::kUmaTargetedHistogramFlag); \
+    histogram->Add(value); \
+  }
+
+#define RPP_PREDICTED_HISTOGRAM_PERCENTAGE(name, value) \
+  { \
+    std::string full_name = prefix + name + suffix; \
+    base::HistogramBase* histogram = base::LinearHistogram::FactoryGet( \
+        full_name, 1, 101, 102, base::Histogram::kUmaTargetedHistogramFlag); \
+    histogram->Add(value); \
+  }
+
+  RPP_PREDICTED_HISTOGRAM_COUNTS("PrefetchCount", num_assumed_prefetched);
+  RPP_PREDICTED_HISTOGRAM_COUNTS("PrefetchMisses_Count", prefetch_missed);
+  RPP_PREDICTED_HISTOGRAM_COUNTS("PrefetchFromCache_Count", prefetch_cached);
+  RPP_PREDICTED_HISTOGRAM_COUNTS("PrefetchFromNetwork_Count", prefetch_network);
+
+  RPP_PREDICTED_HISTOGRAM_PERCENTAGE(
+      "PrefetchMisses_PercentOfTotalPrefetched",
+      prefetch_missed * 100.0 / num_assumed_prefetched);
+  RPP_PREDICTED_HISTOGRAM_PERCENTAGE(
+      "PrefetchFromCache_PercentOfTotalPrefetched",
+      prefetch_cached * 100.0 / num_assumed_prefetched);
+  RPP_PREDICTED_HISTOGRAM_PERCENTAGE(
+      "PrefetchFromNetwork_PercentOfTotalPrefetched",
+      prefetch_network * 100.0 / num_assumed_prefetched);
+
+  // Measure the ratio of total number of resources prefetched from network vs
+  // the total number of resources fetched by the page from the network.
+  if (total_resources_fetched_from_network > 0) {
+    RPP_PREDICTED_HISTOGRAM_PERCENTAGE(
+        "PrefetchFromNetworkPercentOfTotalFromNetwork",
+        prefetch_network * 100.0 / total_resources_fetched_from_network);
+  }
+
+#undef RPP_PREDICTED_HISTOGRAM_PERCENTAGE
+#undef RPP_PREDICTED_HISTOGRAM_COUNTS
+}
+
+}  // namespace predictors