Consolidate serialization code in base::HistogramDeltasSerializer.

base/base.gypi

 # 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.
 
 {
   'target_defaults': {
     'variables': {
       'base_target': 0,
     },
     'target_conditions': [
@@ skipping 321 matching lines @@
           'metrics/sample_map.cc',
           'metrics/sample_map.h',
           'metrics/sample_vector.cc',
           'metrics/sample_vector.h',
           'metrics/bucket_ranges.cc',
           'metrics/bucket_ranges.h',
           'metrics/histogram.cc',
           'metrics/histogram.h',
           'metrics/histogram_base.cc',
           'metrics/histogram_base.h',
+          'metrics/histogram_delta_serialization.cc',
+          'metrics/histogram_delta_serialization.h',
           'metrics/histogram_flattener.h',
           'metrics/histogram_samples.cc',
           'metrics/histogram_samples.h',
           'metrics/histogram_snapshot_manager.cc',
           'metrics/histogram_snapshot_manager.h',
           'metrics/sparse_histogram.cc',
           'metrics/sparse_histogram.h',
           'metrics/statistics_recorder.cc',
           'metrics/statistics_recorder.h',
           'metrics/stats_counters.cc',
@@ skipping 563 matching lines @@
           ['<(toolkit_uses_gtk) == 1', {
             'sources!': [
               'x11/x11_error_tracker.cc',
             ],
           }],
         ],
       }],
     ],
   },
 }