Update from https://crrev.com/316786

base/metrics/stats_counters.h

-// Copyright (c) 2011 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 BASE_METRICS_STATS_COUNTERS_H_
-#define BASE_METRICS_STATS_COUNTERS_H_
-
-#include <string>
-
-#include "base/base_export.h"
-#include "base/compiler_specific.h"
-#include "base/metrics/stats_table.h"
-#include "base/time/time.h"
-
-namespace base {
-
-// StatsCounters are dynamically created values which can be tracked in
-// the StatsTable.  They are designed to be lightweight to create and
-// easy to use.
-//
-// Since StatsCounters can be created dynamically by name, there is
-// a hash table lookup to find the counter in the table.  A StatsCounter
-// object can be created once and used across multiple threads safely.
-//
-// Example usage:
-//    {
-//      StatsCounter request_count("RequestCount");
-//      request_count.Increment();
-//    }
-//
-// Note that creating counters on the stack does work, however creating
-// the counter object requires a hash table lookup.  For inner loops, it
-// may be better to create the counter either as a member of another object
-// (or otherwise outside of the loop) for maximum performance.
-//
-// Internally, a counter represents a value in a row of a StatsTable.
-// The row has a 32bit value for each process/thread in the table and also
-// a name (stored in the table metadata).
-//
-// NOTE: In order to make stats_counters usable in lots of different code,
-// avoid any dependencies inside this header file.
-//
-
-//------------------------------------------------------------------------------
-// Define macros for ease of use. They also allow us to change definitions
-// as the implementation varies, or depending on compile options.
-//------------------------------------------------------------------------------
-// First provide generic macros, which exist in production as well as debug.
-#define STATS_COUNTER(name, delta) do { \
-  base::StatsCounter counter(name); \
-  counter.Add(delta); \
-} while (0)
-
-#define SIMPLE_STATS_COUNTER(name) STATS_COUNTER(name, 1)
-
-#define RATE_COUNTER(name, duration) do { \
-  base::StatsRate hit_count(name); \
-  hit_count.AddTime(duration); \
-} while (0)
-
-// Define Debug vs non-debug flavors of macros.
-#ifndef NDEBUG
-
-#define DSTATS_COUNTER(name, delta) STATS_COUNTER(name, delta)
-#define DSIMPLE_STATS_COUNTER(name) SIMPLE_STATS_COUNTER(name)
-#define DRATE_COUNTER(name, duration) RATE_COUNTER(name, duration)
-
-#else  // NDEBUG
-
-#define DSTATS_COUNTER(name, delta) do {} while (0)
-#define DSIMPLE_STATS_COUNTER(name) do {} while (0)
-#define DRATE_COUNTER(name, duration) do {} while (0)
-
-#endif  // NDEBUG
-
-//------------------------------------------------------------------------------
-// StatsCounter represents a counter in the StatsTable class.
-class BASE_EXPORT StatsCounter {
- public:
-  // Create a StatsCounter object.
-  explicit StatsCounter(const std::string& name);
-  virtual ~StatsCounter();
-
-  // Sets the counter to a specific value.
-  void Set(int value);
-
-  // Increments the counter.
-  void Increment() {
-    Add(1);
-  }
-
-  virtual void Add(int value);
-
-  // Decrements the counter.
-  void Decrement() {
-    Add(-1);
-  }
-
-  void Subtract(int value) {
-    Add(-value);
-  }
-
-  // Is this counter enabled?
-  // Returns false if table is full.
-  bool Enabled() {
-    return GetPtr() != NULL;
-  }
-
-  int value() {
-    int* loc = GetPtr();
-    if (loc) return *loc;
-    return 0;
-  }
-
- protected:
-  StatsCounter();
-
-  // Returns the cached address of this counter location.
-  int* GetPtr();
-
-  std::string name_;
-  // The counter id in the table.  We initialize to -1 (an invalid value)
-  // and then cache it once it has been looked up.  The counter_id is
-  // valid across all threads and processes.
-  int32 counter_id_;
-};
-
-
-// A StatsCounterTimer is a StatsCounter which keeps a timer during
-// the scope of the StatsCounterTimer.  On destruction, it will record
-// its time measurement.
-class BASE_EXPORT StatsCounterTimer : protected StatsCounter {
- public:
-  // Constructs and starts the timer.
-  explicit StatsCounterTimer(const std::string& name);
-  ~StatsCounterTimer() override;
-
-  // Start the timer.
-  void Start();
-
-  // Stop the timer and record the results.
-  void Stop();
-
-  // Returns true if the timer is running.
-  bool Running();
-
-  // Accept a TimeDelta to increment.
-  virtual void AddTime(TimeDelta time);
-
- protected:
-  // Compute the delta between start and stop, in milliseconds.
-  void Record();
-
-  TimeTicks start_time_;
-  TimeTicks stop_time_;
-};
-
-// A StatsRate is a timer that keeps a count of the number of intervals added so
-// that several statistics can be produced:
-//    min, max, avg, count, total
-class BASE_EXPORT StatsRate : public StatsCounterTimer {
- public:
-  // Constructs and starts the timer.
-  explicit StatsRate(const std::string& name);
-  ~StatsRate() override;
-
-  void Add(int value) override;
-
- private:
-  StatsCounter counter_;
-  StatsCounter largest_add_;
-};
-
-
-// Helper class for scoping a timer or rate.
-template<class T> class StatsScope {
- public:
-  explicit StatsScope<T>(T& timer)
-      : timer_(timer) {
-    timer_.Start();
-  }
-
-  ~StatsScope() {
-    timer_.Stop();
-  }
-
-  void Stop() {
-    timer_.Stop();
-  }
-
- private:
-  T& timer_;
-};
-
-}  // namespace base
-
-#endif  // BASE_METRICS_STATS_COUNTERS_H_