Add UMA Histogram Manager to Cronet.

components/metrics/BUILD.gn

 # 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.
 
 # GYP version: components/metrics.gypi:metrics
 source_set("metrics") {
   sources = [
     "clean_exit_beacon.cc",
     "clean_exit_beacon.h",
     "client_info.cc",
     "client_info.h",
     "cloned_install_detector.cc",
     "cloned_install_detector.h",
     "compression_utils.cc",
     "compression_utils.h",
     "daily_event.cc",
     "daily_event.h",
+    "histogram_encoder.cc",
+    "histogram_encoder.h",
+    "histogram_manager.cc",
+    "histogram_manager.h",
     "machine_id_provider.h",
     "machine_id_provider_stub.cc",
     "machine_id_provider_win.cc",
     "metrics_hashes.cc",
     "metrics_hashes.h",
     "metrics_log.cc",
     "metrics_log.h",
     "metrics_log_manager.cc",
     "metrics_log_manager.h",
     "metrics_log_uploader.cc",
@@ skipping 124 matching lines @@
       "//base",
     ]
   }
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "compression_utils_unittest.cc",
     "daily_event_unittest.cc",
+    "histogram_encoder_unittest.cc",
+    "histogram_manager_unittest.cc",
     "machine_id_provider_win_unittest.cc",
     "metrics_hashes_unittest.cc",
     "metrics_log_manager_unittest.cc",
     "metrics_log_unittest.cc",
     "metrics_reporting_scheduler_unittest.cc",
     "metrics_service_unittest.cc",
     "metrics_state_manager_unittest.cc",
     "persisted_logs_unittest.cc",
     "profiler/profiler_metrics_provider_unittest.cc",
   ]
 
   deps = [
     ":metrics",
     ":profiler",
     ":test_support",
     "//base:prefs_test_support",
     "//base/test:test_support",
     "//components/variations",
     "//content/public/common",
     "//testing/gtest",
   ]
 }
 # TODO(GYP): metrics_chromeos