base: Cleanup class/struct forward declarations

base/metrics/histogram.h

 // Copyright (c) 2012 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.
 
 // Histogram is an object that aggregates statistics, and can summarize them in
 // various forms, including ASCII graphical, HTML, and numerically (as a
 // vector of numbers corresponding to each of the aggregating buckets).
 
 // It supports calls to accumulate either time intervals (which are processed
 // as integral number of milliseconds), or arbitrary integral units.
@@ skipping 74 matching lines @@
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/histogram_samples.h"
 #include "base/time/time.h"
 
 namespace base {
 
 class BooleanHistogram;
 class CustomHistogram;
 class Histogram;
 class LinearHistogram;
-class PersistentMemoryAllocator;
 class Pickle;
 class PickleIterator;
 class SampleVector;
 
 class BASE_EXPORT Histogram : public HistogramBase {
  public:
   // Initialize maximum number of buckets in histograms as 16,384.
   static const uint32_t kBucketCount_MAX;
 
   typedef std::vector<Count> Counts;
@@ skipping 437 matching lines @@
   static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
 
   static bool ValidateCustomRanges(const std::vector<Sample>& custom_ranges);
 
   DISALLOW_COPY_AND_ASSIGN(CustomHistogram);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_H_