Convert test_support source sets to static libs

components/cast_certificate/BUILD.gn

 # Copyright 2016 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.
 
-source_set("cast_certificate") {
+static_library("cast_certificate") {
   sources = [
     "cast_cert_validator.cc",
     "cast_cert_validator.h",
     "cast_root_ca_cert_der-inc.h",
     "eureka_root_ca_der-inc.h",
   ]
   deps = [
     "//base",
     "//net",
   ]
 }
 
-source_set("test_support") {
+static_library("test_support") {
   testonly = true
   sources = [
     "cast_cert_validator_test_helpers.cc",
     "cast_cert_validator_test_helpers.h",
   ]
   deps = [
     ":cast_certificate",
     "//base",
     "//net",
     "//testing/gtest",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "cast_cert_validator_unittest.cc",
   ]
   deps = [
     ":cast_certificate",
     ":test_support",
     "//base",
     "//net",
     "//testing/gtest",
   ]
 }