Revert of Add support for single sample metrics.

base/metrics/single_sample_metrics.h

Index: base/metrics/single_sample_metrics.h
diff --git a/base/metrics/single_sample_metrics.h b/base/metrics/single_sample_metrics.h
deleted file mode 100644
index 6bfd7cb0db10323a9c6e44933cdd4c991c0ac87d..0000000000000000000000000000000000000000
--- a/base/metrics/single_sample_metrics.h
+++ /dev/null
@@ -1,104 +0,0 @@
-// Copyright 2017 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_SINGLE_SAMPLE_METRICS_H_
-#define BASE_METRICS_SINGLE_SAMPLE_METRICS_H_
-
-#include <string>
-
-#include "base/base_export.h"
-#include "base/macros.h"
-#include "base/metrics/histogram_base.h"
-
-namespace base {
-
-// See base/metrics/histograms.h for parameter definitions. Must only be used
-// and destroyed from the same thread as construction.
-class BASE_EXPORT SingleSampleMetric {
- public:
-  virtual ~SingleSampleMetric() {}
-
-  virtual void SetSample(HistogramBase::Sample sample) = 0;
-};
-
-// Factory for creating single sample metrics. A single sample metric only
-// reports its sample once at destruction time. The sample may be changed prior
-// to destruction using the SetSample() method as many times as desired.
-//
-// The metric creation methods are safe to call from any thread, however the
-// returned class must only be used and destroyed from the same thread as
-// construction.
-//
-// See base/metrics/histogram_macros.h for usage recommendations and
-// base/metrics/histogram.h for full parameter definitions.
-class BASE_EXPORT SingleSampleMetricsFactory {
- public:
-  virtual ~SingleSampleMetricsFactory() {}
-
-  // Returns the factory provided by SetFactory(), or if no factory has been set
-  // a default factory will be provided (future calls to SetFactory() will fail
-  // if the default factory is ever vended).
-  static SingleSampleMetricsFactory* Get();
-  static void SetFactory(std::unique_ptr<SingleSampleMetricsFactory> factory);
-
-  // The factory normally persists until process shutdown, but in testing we
-  // should avoid leaking it since it sets a global.
-  static void DeleteFactoryForTesting();
-
-  // The methods below return a single sample metric for counts histograms; see
-  // method comments for the corresponding histogram macro.
-
-  // UMA_HISTOGRAM_CUSTOM_COUNTS()
-  virtual std::unique_ptr<SingleSampleMetric> CreateCustomCountsMetric(
-      const std::string& histogram_name,
-      HistogramBase::Sample min,
-      HistogramBase::Sample max,
-      uint32_t bucket_count) = 0;
-};
-
-// Default implementation for when no factory has been provided to the process.
-// Samples are only recorded within the current process in this case, so samples
-// will be lost in the event of sudden process termination.
-class BASE_EXPORT DefaultSingleSampleMetricsFactory
-    : public SingleSampleMetricsFactory {
- public:
-  DefaultSingleSampleMetricsFactory() {}
-  ~DefaultSingleSampleMetricsFactory() override {}
-
-  // SingleSampleMetricsFactory:
-  std::unique_ptr<SingleSampleMetric> CreateCustomCountsMetric(
-      const std::string& histogram_name,
-      HistogramBase::Sample min,
-      HistogramBase::Sample max,
-      uint32_t bucket_count) override;
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(DefaultSingleSampleMetricsFactory);
-};
-
-class BASE_EXPORT DefaultSingleSampleMetric : public SingleSampleMetric {
- public:
-  DefaultSingleSampleMetric(const std::string& histogram_name,
-                            HistogramBase::Sample min,
-                            HistogramBase::Sample max,
-                            uint32_t bucket_count,
-                            int32_t flags);
-  ~DefaultSingleSampleMetric() override;
-
-  // SingleSampleMetric:
-  void SetSample(HistogramBase::Sample sample) override;
-
- private:
-  HistogramBase* const histogram_;
-
-  // The last sample provided to SetSample(). We use -1 as a sentinel value to
-  // indicate no sample has been set.
-  HistogramBase::Sample sample_ = -1;
-
-  DISALLOW_COPY_AND_ASSIGN(DefaultSingleSampleMetric);
-};
-
-}  // namespace base
-
-#endif  // BASE_METRICS_SINGLE_SAMPLE_METRICS_H_