Adding a previews IO-thread blacklist

components/previews/core/previews_black_list_item.h

Index: components/previews/core/previews_black_list_item.h
diff --git a/components/previews/core/previews_black_list_item.h b/components/previews/core/previews_black_list_item.h
new file mode 100644
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+++ b/components/previews/core/previews_black_list_item.h
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+// 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_CORE_PREVIEWS_BLACK_LIST_ITEM_H_
+#define COMPONENTS_PREVIEWS_CORE_PREVIEWS_BLACK_LIST_ITEM_H_
+
+#include <stdint.h>
+
+#include <list>
+#include <map>
+#include <memory>
+#include <string>
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/optional.h"
+#include "base/time/time.h"
+
+namespace previews {
+
+// Stores the recent black list history for a single host. Stores
+// |stored_history_length| of the most recent previews navigations. To determine
+// previews eligiblity fewer than |opt_out_black_list_threshold| out of the past
+// |stored_history_length| navigations must be opt outs. |black_list_duration|
+// is the amount of time that elapses until the host is no longer on the black
+// list.
+class PreviewsBlackListItem {
+ public:
+  PreviewsBlackListItem(size_t stored_history_length,
+                        int opt_out_black_list_threshold,
+                        base::TimeDelta black_list_duration);
+
+  ~PreviewsBlackListItem();
+
+  // Adds a new navigation at the specified |entry_time|.
+  void AddPreviewNavigation(bool opt_out, base::Time entry_time);
+
+  // Whether the host name corresponding to |this| should be disallowed from
+  // showing previews.
+  bool IsBlackListed(base::Time now) const;
+
+  base::Optional<base::Time> most_recent_opt_out_time() const {
+    return most_recent_opt_out_time_;
+  }
+
+ private:
+  // A previews navigation to this host is represented by time and whether the
+  // navigation was an opt out.
+  struct OptOutRecord {
+    OptOutRecord(base::Time entry_time, bool opt_out);
+    ~OptOutRecord() {}
+    const base::Time
+        entry_time;      // The time that the opt out state was determined.
+    const bool opt_out;  // Whether the user opt out of the preview.
+  };
+
+  // The number of entries to store to determine preview eligibility.
+  const size_t max_stored_history_length_;
+  // The number opt outs in recent history that will trigger blacklisting.
+  const int opt_out_black_list_threshold_;
+  // The amount of time to black list a domain after the most recent opt out.
+  const base::TimeDelta max_black_list_duration_;
+
+  // The |max_stored_history_length_| most recent previews navigation. Is
+  // maintained as a list sorted by entry_time (earliest to latest).
+  std::list<OptOutRecord> opt_out_records_;
+
+  // Time of the most recent opt out.
+  base::Optional<base::Time> most_recent_opt_out_time_;
+
+  // The total number of opt outs currently in |opt_out_records_|.
+  int total_opt_out_;
+
+  DISALLOW_COPY_AND_ASSIGN(PreviewsBlackListItem);
+};
+
+}  // namespace previews
+
+#endif  // COMPONENTS_PREVIEWS_CORE_PREVIEWS_BLACK_LIST_ITEM_H_