Convert some GN test support targets to static libs.

ui/views/mus/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("//build/config/ui.gni")
 import("//mojo/public/mojo_application.gni")
 import("//mojo/public/mojo_application_manifest.gni")
 import("//testing/test.gni")
 import("//tools/grit/repack.gni")
@@ skipping 100 matching lines @@
     "//ui/views/resources",
   ]
 }
 
 group("for_mojo_application") {
   public_deps = [
     ":mus",
   ]
 }
 
-source_set("test_support") {
+static_library("test_support") {
   testonly = true
 
   sources = [
     "../test/native_widget_factory_mus.cc",
     "views_mus_test_suite.cc",
     "views_mus_test_suite.h",
   ]
 
   deps = [
     ":mus",
@@ skipping 170 matching lines @@
   type = "exe"
   application_name = "views_mus_unittests"
   source = "unittests_manifest.json"
 }
 
 mojo_application_manifest("interactive_ui_tests_manifest") {
   type = "exe"
   application_name = "views_mus_interactive_ui_tests"
   source = "interactive_ui_tests_manifest.json"
 }