Expose macros from base/metrics/histogram_macros.h as functions

base/metrics/histogram_functions.h

Index: base/metrics/histogram_functions.h
diff --git a/base/metrics/histogram_functions.h b/base/metrics/histogram_functions.h
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+++ b/base/metrics/histogram_functions.h
@@ -0,0 +1,100 @@
+// 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 BASE_METRICS_HISTOGRAM_FUNCTIONS_H_
+#define BASE_METRICS_HISTOGRAM_FUNCTIONS_H_
+
+#include "base/metrics/histogram.h"
+#include "base/metrics/histogram_base.h"
+#include "base/time/time.h"
+
+// Functions for recording metrics.
+//
+// For best practices on deciding when to emit to a histogram and what form
+// the histogram should take, see
+// https://chromium.googlesource.com/chromium/src.git/+/HEAD/tools/metrics/histograms/README.md
+
+// Functions for recording UMA histograms. These can be used for cases
+// when histogram name is generated at runtime. The functionality is

[Alexei Svitkine (slow), 2016/11/12 01:43:45]

Nit: "when the histogram name"

[nikunjb, 2016/11/12 02:06:53]

Done.

+// equivalent to macros defined in histogram_macros.h for recording histogram.

[Alexei Svitkine (slow), 2016/11/12 01:43:45]

Nit: Remove "for recording histogram"

[nikunjb, 2016/11/12 02:06:53]

Done.

+// Although with flexibility that histogram names and values needn't be
+// constants.

[Alexei Svitkine (slow), 2016/11/12 01:43:45]

Nit: Combine with the previous sentence. Also suggest rewording, e.g.

", but allowing non-constant histogram names."

[nikunjb, 2016/11/12 02:06:53]

Done.

+// These functions are slower compared to their macro equivalent by about a few
+// additional memory lookups. So, these shouldn't be used in performance

[Alexei Svitkine (slow), 2016/11/12 01:43:45]

Nit: "By about a few additional memory lookups" sounds pretty vague and is not
obvious what it means. I suggest either rephrasing to be more precise ("because
the histogram objects are not cached between calls") or just removing the extra
detail.

[nikunjb, 2016/11/12 02:06:53]

Done. Rephrased to add additional comment. I wanted to give the order of speed
difference, so the user can make a judgement when using it (since retrieving
histogram from memory is not exactly a slow operation under normal
circumstances).

+// critical code.
+namespace base {
+
+// For histograms with linear buckets.
+// Used for capturing integer data with a linear bucketing scheme. This can be
+// used when you want the exact value of some small numeric count, with a max of
+// 100 or less. If you need to capture a range of greater than 100, we recommend
+// the use of the COUNT histograms below.
+// Sample usage:
+//   base::UmaHistogramExactLinear("Histogram.Linear", some_value, 10);
+BASE_EXPORT void UmaHistogramExactLinear(
+    const std::string& name, int sample, int value_max);
+
+// For adding sample to enum histogram.
+// Sample usage:
+//   base::UmaHistogramEnumeration("My.Enumeration", VALUE, EVENT_MAX_VALUE);
+// Note that new Enum values can be added, but existing enums must never be
+// renumbered or deleted and reused.
+template <typename T> void UmaHistogramEnumeration(
+    const std::string& name, T sample, T max) {
+    static_assert(
+        std::is_enum<T>::value, "Non enum passed to UmaHistogramEnumeration");
+    return UmaHistogramExactLinear(name, static_cast<int>(sample), max);
+}
+
+// For adding boolean sample to histogram.
+// Sample usage:
+//   base::UmaHistogramBoolean("My.Boolean", true)
+BASE_EXPORT void UmaHistogramBoolean(const std::string& name, bool sample);
+
+// For adding histogram with percent.
+// Percents are integer between 1 and 100.
+// Sample usage:
+//   base::UmaHistogramPercentage("My.Percent", 69)
+BASE_EXPORT void UmaHistogramPercentage(
+    const std::string& name, int percent);
+
+// For adding counts histogram.
+// Sample usage:
+//   base::UmaHistogramCounts("My.Counts", some_value, 1, 600, 30)
+BASE_EXPORT void UmaHistogramCustomCounts(
+    const std::string& name, int sample, int min, int max, int buckets);
+
+// Counts specialization for maximum counts 100, 1000, 10k, 100k, 1M and 10M.
+BASE_EXPORT void UmaHistogramCounts100(const std::string& name, int sample);
+BASE_EXPORT void UmaHistogramCounts1000(const std::string& name, int sample);
+BASE_EXPORT void UmaHistogramCounts10000(const std::string& name, int sample);
+BASE_EXPORT void UmaHistogramCounts100000(const std::string& name, int sample);
+BASE_EXPORT void UmaHistogramCounts1M(const std::string& name, int sample);
+BASE_EXPORT void UmaHistogramCounts10M(const std::string& name, int sample);
+
+// For histograms storing times.
+BASE_EXPORT void UmaHistogramCustomTimes(
+    const std::string& name, TimeDelta sample, TimeDelta min,
+    TimeDelta max, int buckets);
+// For short timings from 1 ms up to 10 seconds (50 buckets).
+BASE_EXPORT void UmaHistogramTimes(const std::string& name, TimeDelta sample);
+// For medium timings up to 3 minutes (50 buckets).
+BASE_EXPORT void UmaHistogramMediumTimes(
+    const std::string& name, TimeDelta sample);
+// For time intervals up to 1 hr (50 buckets).
+BASE_EXPORT void UmaHistogramLongTimes(
+    const std::string& name, TimeDelta sample);
+// For time intervals up to 1 hr (100 buckets).
+BASE_EXPORT void UmaHistogramLongTimes100(
+    const std::string& name, TimeDelta sample);
+
+// For recording memory related histograms.
+// Used to measure common KB-granularity memory stats. Range is up to 500M.
+BASE_EXPORT void UmaHistogramMemoryKB(const std::string& name, int sample);
+// Used to measure common MB-granularity memory stats. Range is up to ~64G.
+BASE_EXPORT void UmaHistogramMemoryLargeMB(const std::string& name, int sample);
+
+}  // namespace base
+
+#endif  // BASE_METRICS_HISTOGRAM_FUNCTIONS_H_