Optimize memory use of registered histograms.

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 <stdint.h>
 
 #include <string>
@@ skipping 74 matching lines @@
     BUCKET_ORDER_ERROR = 0x2,
     COUNT_HIGH_ERROR = 0x4,
     COUNT_LOW_ERROR = 0x8,
 
     NEVER_EXCEEDED_VALUE = 0x10
   };
 
   explicit HistogramBase(const std::string& name);
   virtual ~HistogramBase();
 
-  std::string histogram_name() const { return histogram_name_; }
+  const std::string& histogram_name() const { return histogram_name_; }
 
   // Comapres |name| to the histogram name and triggers a DCHECK if they do not
   // match. This is a helper function used by histogram macros, which results in
   // in more compact machine code being generated by the macros.
   void CheckName(const StringPiece& name) const;
 
   // Operations with Flags enum.
   int32_t flags() const { return flags_; }
   void SetFlags(int32_t flags);
   void ClearFlags(int32_t flags);
@@ skipping 69 matching lines @@
  private:
   const std::string histogram_name_;
   int32_t flags_;
 
   DISALLOW_COPY_AND_ASSIGN(HistogramBase);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_BASE_H_