Adding a previews IO-thread blacklist

components/previews/core/previews_experiments.cc

Index: components/previews/core/previews_experiments.cc
diff --git a/components/previews/core/previews_experiments.cc b/components/previews/core/previews_experiments.cc
index a236ab0bbdfffc7c2f59a14c87718880435567ad..afd1fff87f1ee8db5d3751c94b842d02c69d94ed 100644
--- a/components/previews/core/previews_experiments.cc
+++ b/components/previews/core/previews_experiments.cc
@@ -1,60 +1,124 @@
 // Copyright 2016 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 "components/previews/core/previews_experiments.h"
 
 #include <map>
 #include <string>
 
 #include "base/metrics/field_trial.h"
+#include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "components/variations/variations_associated_data.h"
 
+namespace previews {
+
 namespace {
 
 // The group of client-side previews experiments.
 const char kClientSidePreviewsFieldTrial[] = "ClientSidePreviews";
 
 const char kEnabled[] = "Enabled";
 
 // Allow offline pages to show for prohibitively slow networks.
 const char kOfflinePagesSlowNetwork[] = "show_offline_pages";
 
+// The maximum number of recent previews navigations the black list looks at to
+// determine if a host is blacklisted.
+const char kMaxStoredHistoryLength[] = "stored_history_length";
+
+// The maximum number of hosts allowed in the in memory black list.
+const char kMaxHostsInBlackList[] = "max_hosts_in_blacklist";
+
+// The number of recent navigations that were opted out of that would trigger
+// the host to be blacklisted.
+const char kOptOutThreshold[] = "opt_out_threshold";
+
+// The amount of time a host remains blacklisted due to opt outs.
+const char kBlackListDurationInDays[] = "black_list_duration_in_days";
+
 // The string that corresponds to enabled for the variation param experiments.
 const char kExperimentEnabled[] = "true";
 
+// In seconds. Hosts are blacklisted for 30 days.
+constexpr int kDefaultBlackListDurationInDays = 30;
+
+// Returns the parameter value of |param| as a string. If there is no value for
+// |param|, returns an empty string.
+std::string ParamValue(const std::string& param) {
+  if (!IsIncludedInClientSidePreviewsExperimentsFieldTrial())
+    return std::string();
+  std::map<std::string, std::string> experiment_params;
+  if (!variations::GetVariationParams(kClientSidePreviewsFieldTrial,
+                                      &experiment_params)) {
+    return std::string();
+  }
+  std::map<std::string, std::string>::const_iterator it =
+      experiment_params.find(param);
+  return it == experiment_params.end() ? std::string() : it->second;
+}
+
 }  // namespace
 
-namespace previews {
+namespace params {
+
+size_t MaxStoredHistoryLengthForBlackList() {
+  std::string param_value = ParamValue(kMaxStoredHistoryLength);
+  size_t history_length;
+  if (!base::StringToSizeT(param_value, &history_length)) {
+    return 4;
+  }
+  return history_length;
+}
+
+size_t MaxInMemoryHostsInBlackList() {
+  std::string param_value = ParamValue(kMaxHostsInBlackList);
+  size_t max_hosts;
+  if (!base::StringToSizeT(param_value, &max_hosts)) {
+    return 100;
+  }
+  return max_hosts;
+}
+
+int BlackListOptOutThreshold() {
+  std::string param_value = ParamValue(kOptOutThreshold);
+  int opt_out_threshold;
+  if (!base::StringToInt(param_value, &opt_out_threshold)) {
+    return 2;
+  }
+  return opt_out_threshold;
+}
+
+base::TimeDelta BlackListDuration() {
+  std::string param_value = ParamValue(kBlackListDurationInDays);
+  int duration;
+  if (!base::StringToInt(param_value, &duration)) {
+    return base::TimeDelta::FromDays(kDefaultBlackListDurationInDays);
+  }
+  return base::TimeDelta::FromDays(duration);
+}
+
+}  // namespace params
 
 bool IsIncludedInClientSidePreviewsExperimentsFieldTrial() {
   // By convention, an experiment in the client-side previews study enables use
   // of at least one client-side previews optimization if its name begins with
   // "Enabled."
   return base::StartsWith(
       base::FieldTrialList::FindFullName(kClientSidePreviewsFieldTrial),
       kEnabled, base::CompareCase::SENSITIVE);
 }
 
 bool IsOfflinePreviewsEnabled() {
-  if (!IsIncludedInClientSidePreviewsExperimentsFieldTrial())
-    return false;
-  std::map<std::string, std::string> experiment_params;
-  if (!variations::GetVariationParams(kClientSidePreviewsFieldTrial,
-                                      &experiment_params)) {
-    return false;
-  }
-  std::map<std::string, std::string>::const_iterator it =
-      experiment_params.find(kOfflinePagesSlowNetwork);
-  return it != experiment_params.end() && it->second == kExperimentEnabled;
+  return ParamValue(kOfflinePagesSlowNetwork) == kExperimentEnabled;
 }
 
 bool EnableOfflinePreviewsForTesting() {
   std::map<std::string, std::string> params;
   params[kOfflinePagesSlowNetwork] = kExperimentEnabled;
   return variations::AssociateVariationParams(kClientSidePreviewsFieldTrial,
                                               kEnabled, params) &&
          base::FieldTrialList::CreateFieldTrial(kClientSidePreviewsFieldTrial,
                                                 kEnabled);
 }