Move the test template to //testing/test.gni (part 2)

media/cast/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("//testing/rules.gni")
+
 component("cast") {
   deps = [
     ":sender",
     ":receiver",
   ]
 }
 
 # Common code shared by all cast components.
 source_set("common") {
   sources = [
@@ skipping 349 matching lines @@
   sources = [
     "test/utility/udp_proxy_main.cc",
   ]
 
   deps = [
     ":test_support",
     "//base",
     "//net",
   ]
 }