Extracts CT DNS test utilities into a standalone class

components/certificate_transparency/BUILD.gn

 # Copyright 2015 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.
 
 static_library("certificate_transparency") {
   sources = [
     "ct_policy_manager.cc",
     "ct_policy_manager.h",
     "log_dns_client.cc",
     "log_dns_client.h",
@@ skipping 18 matching lines @@
     "//url",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "ct_policy_manager_unittest.cc",
     "log_dns_client_unittest.cc",
     "log_proof_fetcher_unittest.cc",
+    "mock_log_dns_traffic.cc",
+    "mock_log_dns_traffic.h",
     "single_tree_tracker_unittest.cc",
   ]
-
   deps = [
     ":certificate_transparency",
     "//base/test:test_support",
     "//components/prefs:test_support",
     "//components/safe_json:test_support",
     "//net:test_support",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }