service: Emit trace stats at the end of ReadBuffers

This way, they also include stats about the read of the buffer.
That's particularly useful if the consumer reads only after stopping
the tracing session.

Change-Id: I6e90911a0d02b27071afb2f38a2f688b9ebdecbb
diff --git a/src/tracing/core/tracing_service_impl_unittest.cc b/src/tracing/core/tracing_service_impl_unittest.cc
index d8015cd..ac11ddf 100644
--- a/src/tracing/core/tracing_service_impl_unittest.cc
+++ b/src/tracing/core/tracing_service_impl_unittest.cc
@@ -1347,8 +1347,7 @@
   // SystemInfo
   // Trace read clocksnapshot
   // Trace synchronisation
-  // Trace stats
-  static const int kNumPreamblePackets = 6;
+  static const int kNumPreamblePackets = 5;
   static const int kNumTestPackets = 9;
   static const char kPayload[] = "1234567890abcdef-";