Add UMA Histogram Manager to Cronet.

components/metrics.gypi

 # Copyright 2014 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.
 
 {
   'targets': [
     {
       # GN version: //components/metrics
       'target_name': 'metrics',
       'type': 'static_library',
@@ skipping 15 matching lines @@
         'metrics/clean_exit_beacon.cc',
         'metrics/clean_exit_beacon.h',
         'metrics/client_info.cc',
         'metrics/client_info.h',
         'metrics/cloned_install_detector.cc',
         'metrics/cloned_install_detector.h',
         'metrics/compression_utils.cc',
         'metrics/compression_utils.h',
         'metrics/daily_event.cc',
         'metrics/daily_event.h',
+        'metrics/histogram_encoder.cc',
+        'metrics/histogram_encoder.h',
         'metrics/machine_id_provider.h',
         'metrics/machine_id_provider_stub.cc',
         'metrics/machine_id_provider_win.cc',
         'metrics/metrics_hashes.cc',
         'metrics/metrics_hashes.h',
         'metrics/metrics_log.cc',
         'metrics/metrics_log.h',
         'metrics/metrics_log_manager.cc',
         'metrics/metrics_log_manager.h',
         'metrics/metrics_log_uploader.cc',
@@ skipping 157 matching lines @@
             'metrics/serialization/metric_sample.h',
           ],
           'dependencies': [
             '../base/base.gyp:base',
           ],
         },
       ],
     }],
   ],
 }