Add metrics for DHCP WPAD feature.

base/metrics/histogram.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.
 
 // Histogram is an object that aggregates statistics, and can summarize them in
 // various forms, including ASCII graphical, HTML, and numerically (as a
 // vector of numbers corresponding to each of the aggregating buckets).
 
 // It supports calls to accumulate either time intervals (which are processed
 // as integral number of milliseconds), or arbitrary integral units.
@@ skipping 90 matching lines @@
     static base::Histogram* counter(NULL); \
     if (!counter) \
       counter = base::Histogram::FactoryTimeGet(name, min, max, bucket_count, \
                                                 base::Histogram::kNoFlags); \
     DCHECK_EQ(name, counter->histogram_name()); \
     if ((sample) < (max)) counter->AddTime(sample); \
   } while (0)
 
 // Support histograming of an enumerated value.  The samples should always be
 // less than boundary_value.
-
 #define HISTOGRAM_ENUMERATION(name, sample, boundary_value) do { \
     static base::Histogram* counter(NULL); \
     if (!counter) \
       counter = base::LinearHistogram::FactoryGet(name, 1, boundary_value, \
           boundary_value + 1, base::Histogram::kNoFlags); \
     DCHECK_EQ(name, counter->histogram_name()); \
     counter->Add(sample); \
   } while (0)
 
+// Support histograming of an enumerated value. Samples should be one of the
+// std::vector<int> list provided via |custom_ranges|. You can use the helper
+// function |base::CustomHistogram::ArrayToCustomRanges(samples, num_samples)|
+// to transform a C-style array of valid sample values to a std::vector<int>.
 #define HISTOGRAM_CUSTOM_ENUMERATION(name, sample, custom_ranges) do { \
     static base::Histogram* counter(NULL); \
     if (!counter) \
       counter = base::CustomHistogram::FactoryGet(name, custom_ranges, \
                                                   base::Histogram::kNoFlags); \
     DCHECK_EQ(name, counter->histogram_name()); \
     counter->Add(sample); \
   } while (0)
 
 
@@ skipping 526 matching lines @@
 class BASE_API CustomHistogram : public Histogram {
  public:
 
   static Histogram* FactoryGet(const std::string& name,
                                const std::vector<Sample>& custom_ranges,
                                Flags flags);
 
   // Overridden from Histogram:
   virtual ClassType histogram_type() const;
 
+  // Helper method for transforming an array of valid enumeration values
+  // to the std::vector<int> expected by HISTOGRAM_CUSTOM_ENUMERATION.
+  // This function ensures that a guard bucket exists right after any
+  // valid sample value (unless the next higher sample is also a valid value),
+  // so that invalid samples never fall into the same bucket as valid samples.
+  static std::vector<Sample> ArrayToCustomRanges(const Sample* values,
+                                                 size_t num_values);
+
  protected:
   CustomHistogram(const std::string& name,
                   const std::vector<Sample>& custom_ranges);
 
   // Initialize ranges_ mapping.
   void InitializedCustomBucketRange(const std::vector<Sample>& custom_ranges);
   virtual double GetBucketSize(Count current, size_t i) const;
 
   DISALLOW_COPY_AND_ASSIGN(CustomHistogram);
 };
@@ skipping 56 matching lines @@
 
   // Dump all known histograms to log.
   static bool dump_on_exit_;
 
   DISALLOW_COPY_AND_ASSIGN(StatisticsRecorder);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_H_