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

base/metrics/persistent_histogram_allocator.cc

 // 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.
 
 #include "base/metrics/persistent_histogram_allocator.h"
 
 #include <memory>
 
 #include "base/files/important_file_writer.h"
 #include "base/lazy_instance.h"
@@ skipping 695 matching lines @@
   }
 
   g_allocator = nullptr;
   return WrapUnique(histogram_allocator);
 };
 
 void GlobalHistogramAllocator::SetPersistentLocation(const FilePath& location) {
   persistent_location_ = location;
 }
 
+const FilePath& GlobalHistogramAllocator::GetPersistentLocation() const {
+  return persistent_location_;
+}
+
 bool GlobalHistogramAllocator::WriteToPersistentLocation() {
 #if defined(OS_NACL)
   // NACL doesn't support file operations, including ImportantFileWriter.
   NOTREACHED();
   return false;
 #else
   // Stop if no destination is set.
   if (persistent_location_.empty()) {
     NOTREACHED() << "Could not write \"" << Name() << "\" persistent histograms"
                  << " to file because no location was set.";
@@ skipping 32 matching lines @@
   while (true) {
     std::unique_ptr<HistogramBase> histogram =
         import_iterator_.GetNextWithIgnore(record_to_ignore);
     if (!histogram)
       break;
     StatisticsRecorder::RegisterOrDeleteDuplicate(histogram.release());
   }
 }
 
 }  // namespace base