Use source_set rather than static_library

sky/scheduler/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.
 
-static_library("scheduler") {
+source_set("scheduler") {
   sources = [
     "scheduler.cc",
     "scheduler.h",
     "time_interval.cc",
     "time_interval.h",
     "timer.cc",
     "timer.h",
   ]
 
   deps = [
     "//base",
   ]
 }