Adding a previews IO-thread blacklist

components/previews/previews_black_list_item.cc

+// 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/previews_black_list_item.h"
+
+#include <algorithm>
+
+#include "components/previews/previews_opt_out_store.h"
+
+namespace previews {
+
+PreviewsBlackListItem::PreviewsBlackListItem(
+    size_t stored_history_length,
+    int opt_out_black_list_threshold,
+    base::TimeDelta black_list_duration)
+    : stored_history_length_(stored_history_length),
+      opt_out_black_list_threshold_(opt_out_black_list_threshold),
+      black_list_duration_(black_list_duration),
+      total_opt_out_(0) {}
+
+PreviewsBlackListItem::~PreviewsBlackListItem() {}
+
+void PreviewsBlackListItem::AddPreviewNavigation(bool opt_out,
+                                                 base::Time entry_time) {
+  DCHECK_LE(opt_out_history_.size(), stored_history_length_);
+  if (!most_recent_opt_out_time_ ||
+      entry_time > most_recent_opt_out_time_.value()) {
+    most_recent_opt_out_time_ = entry_time;
+  }
+  total_opt_out_ += opt_out ? 1 : 0;
+
+  // Find insert postion to keep the list sorted. Typically, this will be at the
+  // end of the list, but for systems with clocks that are not non-decreasing
+  // with time, this may not be the end. Linearly search from end to begin.
+  auto iter = opt_out_history_.rbegin();
+  while (iter != opt_out_history_.rend() && iter->entry_time > entry_time) {
+    iter++;
+  }
+  TimeOptOut time_opt_out;
+  time_opt_out.entry_time = entry_time;
+  time_opt_out.opt_out = opt_out;
+  opt_out_history_.insert(iter.base(), time_opt_out);
+
+  // Remove the oldest entry if the size exceeds the history size.
+  if (opt_out_history_.size() > stored_history_length_) {
+    total_opt_out_ -= opt_out_history_.front().opt_out ? 1 : 0;
+    opt_out_history_.pop_front();
+  }
+}
+
+bool PreviewsBlackListItem::IsBlackListed(base::Time now) const {
+  DCHECK_LE(opt_out_history_.size(), stored_history_length_);
+  return most_recent_opt_out_time_ &&
+         now - most_recent_opt_out_time_.value() < black_list_duration_ &&
+         total_opt_out_ >= opt_out_black_list_threshold_;
+}
+
+}  // namespace previews