base: Cleanup class/struct forward declarations

base/metrics/statistics_recorder.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.
 
 // StatisticsRecorder holds all Histograms and BucketRanges that are used by
 // Histograms in the system. It provides a general place for
 // Histograms/BucketRanges to register, and supports a global API for accessing
 // (i.e., dumping, or graphing) the data.
 
 #ifndef BASE_METRICS_STATISTICS_RECORDER_H_
 #define BASE_METRICS_STATISTICS_RECORDER_H_
 
 #include <stdint.h>
 
 #include <list>
 #include <map>
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/gtest_prod_util.h"
 #include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/metrics/histogram_base.h"
 #include "base/strings/string_piece.h"
 
-class SubprocessMetricsProviderTest;
-
 namespace base {
 
 class BucketRanges;
 class Lock;
 
 class BASE_EXPORT StatisticsRecorder {
  public:
   // A class used as a key for the histogram map below. It always references
   // a string owned outside of this class, likely in the value of the map.
   class StringKey : public StringPiece {
@@ skipping 193 matching lines @@
 
   // Lock protects access to above maps.
   static base::Lock* lock_;
 
   DISALLOW_COPY_AND_ASSIGN(StatisticsRecorder);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_STATISTICS_RECORDER_H_