Return a NULL histogram pointer on construction error

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 <string>
 #include <vector>
 
@@ skipping 61 matching lines @@
   enum Inconsistency {
     NO_INCONSISTENCIES = 0x0,
     RANGE_CHECKSUM_ERROR = 0x1,
     BUCKET_ORDER_ERROR = 0x2,
     COUNT_HIGH_ERROR = 0x4,
     COUNT_LOW_ERROR = 0x8,
 
     NEVER_EXCEEDED_VALUE = 0x10
   };
 
+  enum ConstructionBehavior {
+    kDoNotAllowBadConstruction = 0,
+    kAllowBadConstruction = 1
+  };
+
   explicit HistogramBase(const std::string& name);
   virtual ~HistogramBase();
 
   std::string histogram_name() const { return histogram_name_; }
 
   // Operations with Flags enum.
   int32 flags() const { return flags_; }
   void SetFlags(int32 flags);
   void ClearFlags(int32 flags);
 
@@ skipping 68 matching lines @@
  private:
   const std::string histogram_name_;
   int32 flags_;
 
   DISALLOW_COPY_AND_ASSIGN(HistogramBase);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_BASE_H_