components/metrics: Add runtime memory leak detector

components/metrics/leak_detector/ranked_list.h

+// Copyright 2015 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_METRICS_LEAK_DETECTOR_RANKED_LIST_H_
+#define COMPONENTS_METRICS_LEAK_DETECTOR_RANKED_LIST_H_
+
+#include <stddef.h>
+
+#include <list>
+
+#include "base/macros.h"
+#include "base/move.h"
+#include "components/metrics/leak_detector/custom_allocator.h"
+#include "components/metrics/leak_detector/leak_detector_value_type.h"
+#include "components/metrics/leak_detector/stl_allocator.h"
+
+namespace metrics {
+namespace leak_detector {
+
+// RankedList lets you add entries consisting of a value-count pair, and
+// automatically sorts them internally by count in descending order. This allows
+// for the user of this list to put value-count pairs into this list without
+// having to explicitly sort them by count.
+class RankedList {
+  MOVE_ONLY_TYPE_FOR_CPP_03(RankedList, RValue);
+
+ public:
+  using ValueType = LeakDetectorValueType;
+
+  // A single entry in the RankedList. The RankedList sorts entries by |count|
+  // in descending order.
+  struct Entry {
+    ValueType value;
+    int count;
+
+    // Create a < comparator for reverse sorting.
+    bool operator<(Entry& entry) const { return count > entry.count; }
+  };
+
+  using EntryList = std::list<Entry, STLAllocator<Entry, CustomAllocator>>;
+  using const_iterator = EntryList::const_iterator;
+
+  explicit RankedList(size_t max_size) : max_size_(max_size) {}
+
+  // For move semantics.
+  RankedList(RValue other);
+  RankedList& operator=(RValue other);
+
+  // Accessors for begin() and end() const iterators.
+  const_iterator begin() const { return entries_.begin(); }
+  const_iterator end() const { return entries_.end(); }
+
+  size_t size() const { return entries_.size(); }
+  size_t max_size() const { return max_size_; }
+
+  // Add a new value-count pair to the list. Does not check for existing entries
+  // with the same value. Is an O(n) operation due to ordering.
+  void Add(const ValueType& value, int count);
+
+ private:
+  // Max and min counts. Returns 0 if the list is empty.
+  const int max_count() const {
+    return entries_.empty() ? 0 : entries_.begin()->count;
+  }
+  const int min_count() const {
+    return entries_.empty() ? 0 : entries_.rbegin()->count;
+  }
+
+  // Max number of items that can be stored in the list.
+  size_t max_size_;
+
+  // Points to the array of entries.
+  std::list<Entry, STLAllocator<Entry, CustomAllocator>> entries_;
+};
+
+}  // namespace leak_detector
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_LEAK_DETECTOR_RANKED_LIST_H_