[Tracing Clock Sync] Add TracingAgent interface in Chrome

base/trace_event/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("trace_event") {
   sources = [
     "common/trace_event_common.h",
     "heap_profiler_allocation_context.cc",
     "heap_profiler_allocation_context.h",
     "heap_profiler_allocation_context_tracker.cc",
@@ skipping 46 matching lines @@
     "trace_event_memory_overhead.h",
     "trace_event_synthetic_delay.cc",
     "trace_event_synthetic_delay.h",
     "trace_event_system_stats_monitor.cc",
     "trace_event_system_stats_monitor.h",
     "trace_log.cc",
     "trace_log.h",
     "trace_log_constants.cc",
     "trace_sampling_thread.cc",
     "trace_sampling_thread.h",
+    "tracing_agent.cc",
+    "tracing_agent.h",
     "winheap_dump_provider_win.cc",
     "winheap_dump_provider_win.h",
   ]
 
   if (is_nacl) {
     sources -= [
       "process_memory_totals_dump_provider.cc",
       "trace_event_system_stats_monitor.cc",
     ]
   }
@@ skipping 57 matching lines @@
   if (is_linux || is_android) {
     sources += [ "process_memory_maps_dump_provider_unittest.cc" ]
   }
 
   deps = [
     "//base/test:test_support",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }