Return a NULL histogram pointer on construction error

base/metrics/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.
 
 // 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 658 matching lines @@
       PickleIterator* iter);
   static HistogramBase* DeserializeInfoImpl(PickleIterator* iter);
 
   static bool ValidateCustomRanges(const std::vector<Sample>& custom_ranges);
   static BucketRanges* CreateBucketRangesFromCustomRanges(
       const std::vector<Sample>& custom_ranges);
 
   DISALLOW_COPY_AND_ASSIGN(CustomHistogram);
 };
 
+
+// DummyHistogram is an object that overrides Histogram's Add* functions
+// to provide no functionality. This can be returned in the case of mismatched
+// construction arguments to any of the other Histograms' FactoryGet calls.
+class BASE_EXPORT DummyHistogram : public Histogram {

[Alexei Svitkine (slow), 2014/01/17 15:40:13]

I would actually define this class in an anon namespace in histogram.cc.

[elijahtaylor1, 2014/01/17 20:04:16]

Done.

+ public:
+  virtual void Add(Sample value) OVERRIDE {}
+  virtual void AddSamples(const HistogramSamples& samples) OVERRIDE {}
+  virtual bool AddSamplesFromPickle(PickleIterator* iter) OVERRIDE;
+
+  DummyHistogram();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(DummyHistogram);
+};
+
+
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_H_