Refactor histogram_persistence to be a class.

base/metrics/histogram_persistence.h

-// Copyright (c) 2015 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 "base/base_export.h"
-#include "base/feature_list.h"
-#include "base/memory/scoped_ptr.h"
-#include "base/metrics/histogram_base.h"
-#include "base/metrics/persistent_memory_allocator.h"
-
-namespace base {
-
-// Feature definition for enabling histogram persistence.
-BASE_EXPORT extern const Feature kPersistentHistogramsFeature;
-
-// Histogram containing creation results. Visible for testing.
-BASE_EXPORT HistogramBase* GetCreateHistogramResultHistogram();
-
-// Access a PersistentMemoryAllocator for storing histograms in space that
-// can be persisted or shared between processes. There is only ever one
-// allocator for all such histograms created by a single process though one
-// process may access the histograms created by other processes if it has a
-// handle on its memory segment. This takes ownership of the object and
-// should not be changed without great care as it is likely that there will
-// be pointers to data held in that space. It should be called as soon as
-// possible during startup to capture as many histograms as possible and
-// while operating single-threaded so there are no race-conditions.
-BASE_EXPORT void SetPersistentHistogramMemoryAllocator(
-    PersistentMemoryAllocator* allocator);
-BASE_EXPORT PersistentMemoryAllocator* GetPersistentHistogramMemoryAllocator();
-
-// 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.
-BASE_EXPORT PersistentMemoryAllocator*
-ReleasePersistentHistogramMemoryAllocatorForTesting();
-
-// Recreate a Histogram from data held in persistent memory. Though this
-// object will be local to the current process, the sample data will be
-// shared with all other threads referencing it. This method takes a |ref|
-// to the top- level histogram data and the |allocator| on which it is found.
-// This method will return nullptr if any problem is detected with the data.
-// The |allocator| may or may not be the same as the PersistentMemoryAllocator
-// set for general use so that this method can be used to extract Histograms
-// from persistent memory segments other than the default place that this
-// process is creating its own histograms. The caller must take ownership of
-// the returned object and destroy it when no longer needed.
-BASE_EXPORT HistogramBase* GetPersistentHistogram(
-    PersistentMemoryAllocator* allocator,
-    int32_t ref);
-
-// Get the next histogram in persistent data based on iterator. The caller
-// must take ownership of the returned object and destroy it when no longer
-// needed.
-BASE_EXPORT HistogramBase* GetNextPersistentHistogram(
-    PersistentMemoryAllocator* allocator,
-    PersistentMemoryAllocator::Iterator* iter);
-
-// Finalize the creation of the histogram, making it available to other
-// processes if it is the registered instance.
-void FinalizePersistentHistogram(PersistentMemoryAllocator::Reference ref,
-                                 bool register);
-
-// Allocate a new persistent histogram. This does *not* make the object
-// iterable in the allocator; call MakeIterable(ref) directly if that is
-// desired.
-BASE_EXPORT HistogramBase* AllocatePersistentHistogram(
-    PersistentMemoryAllocator* allocator,
-    HistogramType histogram_type,
-    const std::string& name,
-    int minimum,
-    int maximum,
-    const BucketRanges* bucket_ranges,
-    int32_t flags,
-    PersistentMemoryAllocator::Reference* ref_ptr);
-
-// Import new histograms from attached PersistentMemoryAllocator. It's
-// possible for other processes to create histograms in the attached memory
-// segment; this adds those to the internal list of known histograms to
-// avoid creating duplicates that would have to merged during reporting.
-// Every call to this method resumes from the last entry it saw so it costs
-// nothing if nothing new has been added.
-void ImportPersistentHistograms();
-
-}  // namespace base
-
-#endif  // BASE_METRICS_HISTOGRAM_PERSISTENCE_H_