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

webrtc/test/test_main.cc

 /*
  *  Copyright (c) 2013 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.
  */
 
 #include "gflags/gflags.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "webrtc/base/logging.h"
+#include "webrtc/system_wrappers/include/metrics_default.h"
 #include "webrtc/test/field_trial.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 DEFINE_string(force_fieldtrials, "",
     "Field trials control experimental feature code which can be forced. "
     "E.g. running with --force_fieldtrials=WebRTC-FooFeature/Enable/"
     " will assign the group Enable to field trial WebRTC-FooFeature.");
 
 int main(int argc, char* argv[]) {
   ::testing::InitGoogleTest(&argc, argv);
 
   // Default to LS_INFO, even for release builds to provide better test logging.
   // TODO(pbos): Consider adding a command-line override.
   if (rtc::LogMessage::GetLogToDebug() > rtc::LS_INFO)
     rtc::LogMessage::LogToDebug(rtc::LS_INFO);
 
   // AllowCommandLineParsing allows us to ignore flags passed on to us by
   // Chromium build bots without having to explicitly disable them.
   google::AllowCommandLineReparsing();
   google::ParseCommandLineFlags(&argc, &argv, false);
 
   webrtc::test::SetExecutablePath(argv[0]);
   webrtc::test::InitFieldTrialsFromString(FLAGS_force_fieldtrials);
+  webrtc::metrics::Enable();
   return RUN_ALL_TESTS();
 }