[Tracing] Update sync_id to be string type for clock sync

base/trace_event/tracing_agent.h

Index: base/trace_event/tracing_agent.h
diff --git a/base/trace_event/tracing_agent.h b/base/trace_event/tracing_agent.h
index 77183b0d123c46dba163daf239fcb5ea033a12a1..db8d122bea8474b4e3c0a2382d8ae951da80e288 100644
--- a/base/trace_event/tracing_agent.h
+++ b/base/trace_event/tracing_agent.h
@@ -35,7 +35,7 @@ class BASE_EXPORT TracingAgent {
       const std::string& events_label,
       const scoped_refptr<base::RefCountedString>& events_str_ptr)>;
   using RecordClockSyncMarkerCallback = base::Callback<void(
-      int sync_id,
+      const std::string& sync_id,
       const TimeTicks& issue_ts,
       const TimeTicks& issue_end_ts)>;
 
@@ -87,7 +87,7 @@ class BASE_EXPORT TracingAgent {
   // The assumption is that the receiver thread knows the issuer's clock, which
   // is true in Chrome because all agent threads' clocks are Chrome clock.
   virtual void RecordClockSyncMarker(
-      int sync_id,
+      const std::string& sync_id,
       const RecordClockSyncMarkerCallback& callback);
 };