Refactor of Histogram related code

base/metrics/histogram_base.h

 // Copyright (c) 2012 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_BASE_H_
 #define BASE_METRICS_HISTOGRAM_BASE_H_
 
 #include <climits>
 #include <string>
 
 #include "base/base_export.h"
 
 namespace base {
 
 class BASE_EXPORT HistogramBase {
  public:
   typedef int Sample;  // Used for samples.
   typedef int Count;   // Used to count samples.
 
-  static const Sample kSampleType_MAX = INT_MAX;
+  static const Sample kSampleType_MAX;  // INT_MAX
 
   HistogramBase(const std::string& name);
   virtual ~HistogramBase();
 
   std::string histogram_name() const { return histogram_name_; }
 
   virtual void Add(Sample value) = 0;
 
   // The following methods provide graphical histogram displays.
   virtual void WriteHTMLGraph(std::string* output) const = 0;
   virtual void WriteAscii(std::string* output) const = 0;
 
  private:
   const std::string histogram_name_;
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_BASE_H_