Add support for periodic flushes

Adds a new |fush_period_ms| field to the TraceConfig.
When set, it causes the trace service to issue periodic
flush requests to all data sources.

Bug: 73886018
Change-Id: Ie40fa83b811c8115cf27fd1034262610ca8b4a81
diff --git a/src/tracing/core/tracing_service_impl.h b/src/tracing/core/tracing_service_impl.h
index 685bad6..d2f97ae 100644
--- a/src/tracing/core/tracing_service_impl.h
+++ b/src/tracing/core/tracing_service_impl.h
@@ -311,6 +311,7 @@
   void OnFlushTimeout(TracingSessionID, FlushRequestID);
   void OnDisableTracingTimeout(TracingSessionID);
   void DisableTracingNotifyConsumerAndFlushFile(TracingSession*);
+  void PeriodicFlushTask(TracingSessionID, bool post_next_only);
   TraceBuffer* GetBufferByID(BufferID);
 
   base::TaskRunner* const task_runner_;