Add a default implementation in metrics_default.cc of histograms methods in system_wrappers/interfac

webrtc/system_wrappers/BUILD.gn

 # Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("//build/config/android/config.gni")
 import("../build/webrtc.gni")
@@ skipping 130 matching lines @@
     "include/field_trial_default.h",
     "source/field_trial_default.cc",
   ]
 
   configs += [ "..:common_config" ]
   public_configs = [ "..:common_inherited_config" ]
 }
 
 source_set("metrics_default") {
   sources = [
+    "include/metrics_default.h",
     "source/metrics_default.cc",
   ]
 
   configs += [ "..:common_config" ]
   public_configs = [ "..:common_inherited_config" ]
 }
 
 source_set("system_wrappers_default") {
   configs += [ "..:common_config" ]
   public_configs = [ "..:common_inherited_config" ]
@@ skipping 22 matching lines @@
 if (is_linux) {
   source_set("cpu_features_linux") {
     sources = [
       "source/cpu_features_linux.c",
     ]
 
     configs += [ "..:common_config" ]
     public_configs = [ "..:common_inherited_config" ]
   }
 }