base: Cleanup class/struct forward declarations

base/metrics/persistent_sample_map.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.
 
 // PersistentSampleMap implements HistogramSamples interface. It is used
 // by the SparseHistogram class to store samples in persistent memory which
 // allows it to be shared between processes or live across restarts.
 
 #ifndef BASE_METRICS_PERSISTENT_SAMPLE_MAP_H_
 #define BASE_METRICS_PERSISTENT_SAMPLE_MAP_H_
 
 #include <stdint.h>
 
 #include <map>
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/metrics/histogram_base.h"
 #include "base/metrics/histogram_samples.h"
 #include "base/metrics/persistent_memory_allocator.h"
 
 namespace base {
 
 class PersistentHistogramAllocator;
 class PersistentSampleMapRecords;
-class PersistentSparseHistogramDataManager;
 
 // The logic here is similar to that of SampleMap but with different data
 // structures. Changes here likely need to be duplicated there.
 class BASE_EXPORT PersistentSampleMap : public HistogramSamples {
  public:
   // Constructs a persistent sample map using a PersistentHistogramAllocator
   // as the data source for persistent records.
   PersistentSampleMap(uint64_t id,
                       PersistentHistogramAllocator* allocator,
                       Metadata* meta);
@@ skipping 63 matching lines @@
   // live beyond the life of this object. This value is lazily-initialized on
   // first use via the GetRecords() accessor method.
   PersistentSampleMapRecords* records_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(PersistentSampleMap);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_PERSISTENT_SAMPLE_MAP_H_