Fix device_event_log component build, make NonThreadSafe (Take 2)

components/device_event_log/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("device_event_log") {
+component("device_event_log") {
   sources = [
     "device_event_log.cc",
     "device_event_log.h",
     "device_event_log_impl.cc",
     "device_event_log_impl.h",
   ]
 
+  defines = [ "DEVICE_EVENT_LOG_IMPLEMENTATION" ]
+
   deps = [
     "//base",
     "//net",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "device_event_log_impl_unittest.cc",
   ]
 
   deps = [
     ":device_event_log",
     "//testing/gtest",
   ]
 }