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

base/trace_event/tracing_agent.h

 // 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.
 
 #ifndef BASE_TRACE_EVENT_TRACING_AGENT_H_
 #define BASE_TRACE_EVENT_TRACING_AGENT_H_
 
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/memory/ref_counted_memory.h"
@@ skipping 17 matching lines @@
  public:
   using StartAgentTracingCallback =
       base::Callback<void(const std::string& agent_name, bool success)>;
   // Passing a null or empty events_str_ptr indicates that no trace data is
   // available for the specified agent.
   using StopAgentTracingCallback = base::Callback<void(
       const std::string& agent_name,
       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)>;
 
   virtual ~TracingAgent();
 
   // Gets the name of the tracing agent. Each tracing agent's name should be
   // unique.
   virtual std::string GetTracingAgentName() = 0;
 
   // Gets the trace event label of this tracing agent. The label will be used to
@@ skipping 31 matching lines @@
   // Having a reliable timing measurement for the 2nd task requires synchronous
   // function call without any cross-thread or cross-process activity. However,
   // tracing agents in Chrome run in their own threads. Therefore, the issuer
   // needs to dedicate the 2nd task to the receiver to take time measurements
   // in the receiver thread, and the receiver thread needs to pass them back to
   // the issuer in the callback.
   //
   // 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);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_TRACING_AGENT_H_