Add interface to system trace clock.

base/debug/trace_event_impl.cc

Index: base/debug/trace_event_impl.cc
diff --git a/base/debug/trace_event_impl.cc b/base/debug/trace_event_impl.cc
index bd997cf39e5d6bb0ffd0d63cd95cf6effd0c8320..9cf33417e8e1654e47b50e5a390ee94ef637bca0 100644
--- a/base/debug/trace_event_impl.cc
+++ b/base/debug/trace_event_impl.cc
@@ -585,7 +585,7 @@ int TraceLog::AddTraceEvent(char phase,
                             long long threshold,
                             unsigned char flags) {
   DCHECK(name);
-  TimeTicks now = TimeTicks::HighResNow();
+  TimeTicks now = TimeTicks::NowFromSystemTraceTime();
   BufferFullCallback buffer_full_callback_copy;
   int ret_begin_id = -1;
   {
@@ -710,7 +710,7 @@ void TraceLog::AddClockSyncMetadataEvents() {
   // debugfs that takes the written data and pushes it onto the trace
   // buffer. So, to establish clock sync, we write our monotonic clock into that
   // trace buffer.
-  TimeTicks now = TimeTicks::HighResNow();
+  TimeTicks now = TimeTicks::NowFromSystemTraceTime();
 
   double now_in_seconds = now.ToInternalValue() / 1000000.0;
   std::string marker =