Add more components_unittests to GN build

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 = [
     "call_stack_profile_metrics_provider.cc",
     "call_stack_profile_metrics_provider.h",
     "clean_exit_beacon.cc",
@@ skipping 190 matching lines @@
     ":metrics",
     ":net",
     ":profiler",
     ":test_support",
     "//base:prefs_test_support",
     "//base/test:test_support",
     "//components/variations",
     "//content/public/common",
     "//testing/gtest",
   ]
+
+  if (is_linux) {
+    sources += [ "serialization/serialization_utils_unittest.cc" ]
+    deps += [ ":serialization" ]
+  }
 }
 # TODO(GYP): metrics_chromeos