Adds a callback to TracingAgent::StartAgentTracing()

content/browser/tracing/etw_system_event_consumer_win.h

Index: content/browser/tracing/etw_system_event_consumer_win.h
diff --git a/content/browser/tracing/etw_system_event_consumer_win.h b/content/browser/tracing/etw_system_event_consumer_win.h
index 4327365386a2fdc11be989eac93601828386ff11..9a3b2725cb950eb913539abb585b713fd0c29424 100644
--- a/content/browser/tracing/etw_system_event_consumer_win.h
+++ b/content/browser/tracing/etw_system_event_consumer_win.h
@@ -28,8 +28,8 @@ class EtwSystemEventConsumer
   // base::trace_event::TracingAgent implementation.
   std::string GetTracingAgentName() override;
   std::string GetTraceEventLabel() override;
-  bool StartAgentTracing(
-      const base::trace_event::TraceConfig& trace_config) override;
+  void StartAgentTracing(const base::trace_event::TraceConfig& trace_config,
+                         const StartAgentTracingCallback& callback) override;
   void StopAgentTracing(const StopAgentTracingCallback& callback) override;
 
   // Retrieve the ETW consumer instance.