[Tracing Clock Sync] Add TracingAgent interface in Chrome

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/common/trace_event_common.h',
       'trace_event/heap_profiler_allocation_context.cc',
       'trace_event/heap_profiler_allocation_context.h',
       'trace_event/heap_profiler_allocation_context_tracker.cc',
@@ skipping 46 matching lines @@
       'trace_event/trace_event_memory_overhead.h',
       'trace_event/trace_event_synthetic_delay.cc',
       'trace_event/trace_event_synthetic_delay.h',
       'trace_event/trace_event_system_stats_monitor.cc',
       'trace_event/trace_event_system_stats_monitor.h',
       'trace_event/trace_log.cc',
       'trace_event/trace_log.h',
       'trace_event/trace_log_constants.cc',
       'trace_event/trace_sampling_thread.cc',
       'trace_event/trace_sampling_thread.h',
+      'trace_event/tracing_agent.cc',
+      'trace_event/tracing_agent.h',
       'trace_event/winheap_dump_provider_win.cc',
       'trace_event/winheap_dump_provider_win.h',
     ],
     'trace_event_test_sources' : [
       'trace_event/heap_profiler_allocation_context_tracker_unittest.cc',
       'trace_event/heap_profiler_allocation_register_unittest.cc',
       'trace_event/heap_profiler_heap_dump_writer_unittest.cc',
       'trace_event/heap_profiler_stack_frame_deduplicator_unittest.cc',
       'trace_event/java_heap_dump_provider_android_unittest.cc',
       'trace_event/memory_allocator_dump_unittest.cc',
@@ skipping 20 matching lines @@
           'trace_event_sources': [
             'trace_event/process_memory_maps_dump_provider.cc',
           ],
           'trace_event_test_sources' : [
             'trace_event/process_memory_maps_dump_provider_unittest.cc',
           ],
       }],
     ],
   },
 }