Revert "Create and pass shared-histogram-allocator from browser to renderer."

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 <memory>
 
 #include "base/atomicops.h"
@@ skipping 98 matching lines @@
   // IMPORTANT: Callers must update tools/metrics/histograms/histograms.xml
   // with the following histograms:
   //    UMA.PersistentAllocator.name.Allocs
   //    UMA.PersistentAllocator.name.UsedPct
   void CreateTrackingHistograms(StringPiece name);
   void UpdateTrackingHistograms();
 
   // Histogram containing creation results. Visible for testing.
   static HistogramBase* GetCreateHistogramResultHistogram();
 
+  // 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<PersistentHistogramAllocator>
+  ReleaseGlobalAllocatorForTesting();
+
  protected:
   // The structure used to hold histogram data in persistent memory. It is
   // defined and used entirely within the .cc file.
   struct PersistentHistogramData;
 
   // Gets the reference of the last histogram created, used to avoid
   // trying to import what was just created.
   PersistentHistogramAllocator::Reference last_created() {
     return subtle::NoBarrier_Load(&last_created_);
   }
@@ skipping 129 matching lines @@
   // Import always continues from where it left off, making use of a single
   // iterator to continue the work.
   Iterator import_iterator_;
 
   DISALLOW_COPY_AND_ASSIGN(GlobalHistogramAllocator);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_PERSISTENCE_H_