[Media Controls] Add UMA for timeline scrubber

third_party/WebKit/Source/platform/Histogram.h

 // 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 Histogram_h
 #define Histogram_h
 
 #include "base/metrics/histogram_base.h"
 #include "base/metrics/histogram_macros.h"
 #include "platform/PlatformExport.h"
 #include "wtf/CurrentTime.h"
 #include <stdint.h>
 
 namespace base {
 class HistogramBase;
 };
 
 namespace blink {
 
 class PLATFORM_EXPORT CustomCountHistogram {
  public:
+  // Min values should be >=1 as emitted 0s still go into the underflow bucket.
   CustomCountHistogram(const char* name,
                        base::HistogramBase::Sample min,
                        base::HistogramBase::Sample max,
                        int32_t bucketCount);
   void count(base::HistogramBase::Sample);
 
  protected:
   explicit CustomCountHistogram(base::HistogramBase*);
 
   base::HistogramBase* m_histogram;
 };
 
 class PLATFORM_EXPORT BooleanHistogram : public CustomCountHistogram {
  public:
   BooleanHistogram(const char* name);
 };
 
 class PLATFORM_EXPORT EnumerationHistogram : public CustomCountHistogram {
  public:
+  // |boundaryValue| must be strictly greater than samples passed to |count|.
   EnumerationHistogram(const char* name,
                        base::HistogramBase::Sample boundaryValue);
 };
 
 class PLATFORM_EXPORT SparseHistogram {
  public:
   explicit SparseHistogram(const char* name);
 
   void sample(base::HistogramBase::Sample);
 
@@ skipping 27 matching lines @@
 // This macro records all times between 0us and 10 seconds.
 // Do not change this macro without renaming all metrics that use it!
 #define SCOPED_BLINK_UMA_HISTOGRAM_TIMER(name)               \
   DEFINE_STATIC_LOCAL(CustomCountHistogram, scopedUsCounter, \
                       (name, 0, 10000000, 50));              \
   ScopedUsHistogramTimer timer(scopedUsCounter);
 
 }  // namespace blink
 
 #endif  // Histogram_h