Add chrome test support target to GN build.

components/search_engines/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.
 
 import("//build/config/features.gni")
 import("//tools/json_to_struct/json_to_struct.gni")
 
 static_library("search_engines") {
   sources = [
     "default_search_manager.cc",
@@ skipping 54 matching lines @@
     sources += [
       "default_search_policy_handler.cc",
       "default_search_policy_handler.h",
     ]
     deps += [
       "//components/policy",
     ]
   }
 }
 
+source_set("test_support") {
+  testonly = true
+  sources = [
+    "default_search_pref_test_util.cc",
+    "default_search_pref_test_util.h",
+    "testing_search_terms_data.cc",
+    "testing_search_terms_data.h",
+  ]
+
+  deps = [
+    ":search_engines",
+    "//testing/gtest",
+  ]
+}
+
 json_to_struct("prepopulated_engines") {
   visibility = [ ":*" ]
 
   source = "prepopulated_engines.json"
   schema_file = "prepopulated_engines_schema.json"
   namespace = "TemplateURLPrepopulateData"
 }