Convert some GN test support targets to static libs.

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 76 matching lines @@
       "default_search_policy_handler.cc",
       "default_search_policy_handler.h",
     ]
     deps += [
       "//components/policy",
       "//components/policy:policy_component",
     ]
   }
 }
 
-source_set("test_support") {
+static_library("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",
   ]
 
   public_deps = [
     ":search_engines",
@@ skipping 42 matching lines @@
   }
 }
 
 json_to_struct("prepopulated_engines") {
   visibility = [ ":*" ]
 
   source = "prepopulated_engines.json"
   schema_file = "prepopulated_engines_schema.json"
   namespace = "TemplateURLPrepopulateData"
 }