Convert some component source sets to static library

components/variations/service/BUILD.gn

 # Copyright 2015 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("service") {
+static_library("service") {
   sources = [
     "ui_string_overrider.cc",
     "ui_string_overrider.h",
     "variations_service.cc",
     "variations_service.h",
     "variations_service_client.h",
   ]
 
   deps = [
     "//base",
@@ skipping 24 matching lines @@
     "//base/test:test_support",
     "//components/prefs:test_support",
     "//components/variations",
     "//components/variations/proto",
     "//components/web_resource:test_support",
     "//net",
     "//net:test_support",
     "//testing/gtest",
   ]
 }