Add missing (and remove superfluous) 'explicit' from constructors.

base/metrics/sparse_histogram.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_SPARSE_HISTOGRAM_H_
 #define BASE_METRICS_SPARSE_HISTOGRAM_H_
 
 #include <map>
 #include <string>
 
@@ skipping 21 matching lines @@
   virtual bool HasConstructionArguments(Sample minimum,
                                         Sample maximum,
                                         size_t bucket_count) const OVERRIDE;
   virtual void Add(Sample value) OVERRIDE;
   virtual void WriteHTMLGraph(std::string* output) const OVERRIDE;
   virtual void WriteAscii(std::string* output) const OVERRIDE;
   virtual scoped_ptr<HistogramSamples> SnapshotSamples() const OVERRIDE;
 
  private:
   // Clients should always use FactoryGet to create SparseHistogram.
-  SparseHistogram(const std::string& name);
+  explicit SparseHistogram(const std::string& name);
 
   virtual void GetParameters(DictionaryValue* params) const OVERRIDE;
   virtual void GetCountAndBucketData(Count* count,
                                      ListValue* buckets) const OVERRIDE;
 
   friend class SparseHistogramTest;  // For constuctor calling.
 
   // Protects access to |sample_counts_| and |redundant_count_|.
   mutable base::Lock lock_;
   std::map<HistogramBase::Sample, HistogramBase::Count> sample_counts_;
   HistogramBase::Count redundant_count_;
 
   DISALLOW_COPY_AND_ASSIGN(SparseHistogram);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_SPARSE_HISTOGRAM_H_