Return a NULL histogram pointer on construction error

base/metrics/histogram.h

Index: base/metrics/histogram.h
diff --git a/base/metrics/histogram.h b/base/metrics/histogram.h
index 9845362d98aa31cad7557383e2fc1e039ad5f67e..f503b3f1ec6eeba9541bc4f00264075fd0fdc56d 100644
--- a/base/metrics/histogram.h
+++ b/base/metrics/histogram.h
@@ -676,6 +676,23 @@ class BASE_EXPORT CustomHistogram : public Histogram {
   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_