Convert some GN test support targets to static libs.

media/audio/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/linux/pkg_config.gni")
 import("//media/media_options.gni")
 
 # When libpulse is not directly linked, use stubs to allow for dlopening of the
 # binary.
 if (!link_pulseaudio) {
@@ skipping 256 matching lines @@
     packages = [ "libcras" ]
   }
 }
 
 if (use_pulseaudio && link_pulseaudio) {
   pkg_config("libpulse") {
     packages = [ "libpulse" ]
   }
 }
 
-source_set("test_support") {
+static_library("test_support") {
   testonly = true
   sources = [
     "audio_unittest_util.cc",
     "audio_unittest_util.h",
     "mock_audio_manager.cc",
     "mock_audio_manager.h",
     "mock_audio_source_callback.cc",
     "mock_audio_source_callback.h",
     "test_audio_input_controller_factory.cc",
     "test_audio_input_controller_factory.h",
@@ skipping 85 matching lines @@
     ]
   }
 
   if (use_alsa) {
     sources += [
       "alsa/alsa_output_unittest.cc",
       "audio_low_latency_input_output_unittest.cc",
     ]
   }
 }