Adding a previews IO-thread blacklist

components/previews/previews_experiments.h

 // 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.
 
 #ifndef COMPONENTS_PREVIEWS_PREVIEWS_EXPERIMENTS_H_
 #define COMPONENTS_PREVIEWS_PREVIEWS_EXPERIMENTS_H_
 
+#include "base/time/time.h"
+
 namespace previews {
 
+namespace params {
+
+// The number of most recent previews navigations the black list looks at to
+// determine if a domain is blacklisted.
+size_t StoredHistoryLengthForBlackList();
+
+// The number of recent navigations that were opted out of that would trigger
+// the domain to be blacklisted.
+int BlackListOptOutThreshold();
+
+// The amount of time a domain remains blacklisted due to opt outs.
+base::TimeDelta BlackListDuration();
+}
+
 // Returns true if any client-side previews experiment is active.
 bool IsIncludedInClientSidePreviewsExperimentsFieldTrial();
 
 // Returns true if the field trial that should enable offline pages for
 // prohibitvely slow networks is active.
 bool IsOfflinePreviewsEnabled();
 
 // Sets the appropriate state for field trial and variations to imitate the
 // offline pages field trial.
 bool EnableOfflinePreviewsForTesting();
 
 }  // namespace previews
 
 #endif  // COMPONENTS_PREVIEWS_PREVIEWS_EXPERIMENTS_H_