Add lockdown mode.

Bug: 73709863
Change-Id: I7f4eb122d85299d32546694195e0461bb9b47a09
diff --git a/src/tracing/core/service_impl.h b/src/tracing/core/service_impl.h
index 2717d2d..eae6364 100644
--- a/src/tracing/core/service_impl.h
+++ b/src/tracing/core/service_impl.h
@@ -262,6 +262,8 @@
   std::map<TracingSessionID, TracingSession> tracing_sessions_;
   std::map<BufferID, TraceBuffer> buffers_;
 
+  bool lockdown_mode_ = false;
+
   PERFETTO_THREAD_CHECKER(thread_checker_)
 
   base::WeakPtrFactory<ServiceImpl> weak_ptr_factory_;  // Keep at the end.