Convert some component source sets to static library

components/browser_sync/common/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.
 
 import("//build/config/features.gni")
 
-source_set("common") {
+static_library("common") {
   sources = [
     "browser_sync_switches.cc",
     "browser_sync_switches.h",
   ]
 
   deps = [
     "//base",
   ]
 }