[Startup Tracing] Enable startup tracing from config file

base/trace_event/trace_event.gypi

 # 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.
 {
   'variables': {
     'trace_event_sources' : [
       'trace_event/java_heap_dump_provider_android.cc',
       'trace_event/java_heap_dump_provider_android.h',
       'trace_event/memory_allocator_dump.cc',
       'trace_event/memory_allocator_dump.h',
       'trace_event/memory_allocator_dump_guid.cc',
       'trace_event/memory_allocator_dump_guid.h',
       'trace_event/memory_dump_manager.cc',
       'trace_event/memory_dump_manager.h',
       'trace_event/memory_dump_provider.h',
       'trace_event/memory_dump_request_args.h',
       'trace_event/memory_dump_session_state.cc',
       'trace_event/memory_dump_session_state.h',
       'trace_event/process_memory_dump.cc',
       'trace_event/process_memory_dump.h',
       'trace_event/process_memory_maps.cc',
       'trace_event/process_memory_maps.h',
       'trace_event/process_memory_maps_dump_provider.cc',
       'trace_event/process_memory_maps_dump_provider.h',
       'trace_event/process_memory_totals.cc',
       'trace_event/process_memory_totals.h',
       'trace_event/process_memory_totals_dump_provider.cc',
       'trace_event/process_memory_totals_dump_provider.h',
+      'trace_event/startup_tracing.cc',
+      'trace_event/startup_tracing.h',
       'trace_event/trace_config.cc',
       'trace_event/trace_config.h',
       'trace_event/trace_event.h',
       'trace_event/trace_event_android.cc',
       'trace_event/trace_event_argument.cc',
       'trace_event/trace_event_argument.h',
       'trace_event/trace_event_etw_export_win.cc',
       'trace_event/trace_event_etw_export_win.h',
       'trace_event/trace_event_impl.cc',
       'trace_event/trace_event_impl.h',
@@ skipping 30 matching lines @@
       'trace_event/trace_event_argument_unittest.cc',
       'trace_event/trace_event_memory_unittest.cc',
       'trace_event/trace_event_synthetic_delay_unittest.cc',
       'trace_event/trace_event_system_stats_monitor_unittest.cc',
       'trace_event/trace_event_unittest.cc',
       'trace_event/trace_event_win_unittest.cc',
       'trace_event/winheap_dump_provider_win_unittest.cc',
     ],
   },
 }