Support experiment to store persistent metrics in memory-mapped file.

base/metrics/persistent_histogram_allocator.h

 // Copyright 2016 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_PERSISTENCE_H_
 #define BASE_METRICS_HISTOGRAM_PERSISTENCE_H_
 
 #include <map>
 #include <memory>
 
@@ skipping 421 matching lines @@
   // This access to the persistent allocator is only for testing; it extracts
   // the current allocator completely. This allows easy creation of histograms
   // within persistent memory segments which can then be extracted and used in
   // other ways.
   static std::unique_ptr<GlobalHistogramAllocator> ReleaseForTesting();
 
   // Stores a pathname to which the contents of this allocator should be saved
   // in order to persist the data for a later use.
   void SetPersistentLocation(const FilePath& location);
 
+  // Retrieves a previously set pathname to which the contents of this allocator
+  // are to be saved.
+  const FilePath& GetPersistentLocation();
+
   // Writes the internal data to a previously set location. This is generally
   // called when a process is exiting from a section of code that may not know
   // the filesystem. The data is written in an atomic manner. The return value
   // indicates success.
   bool WriteToPersistentLocation();
 
  private:
   friend class StatisticsRecorder;
 
   // Creates a new global histogram allocator.
@@ skipping 14 matching lines @@
 
   // The location to which the data should be persisted.
   FilePath persistent_location_;
 
   DISALLOW_COPY_AND_ASSIGN(GlobalHistogramAllocator);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_PERSISTENCE_H_