I see the following in my console when launching content shell:
[09:14:04]:~/Desktop/chromium/src $ ./out/Debug/Content\ Shell.app/Contents/MacOS/Content\ Shell --enable-blink-gen-property-trees file:///Users/pdr/Downloads/dino.html
...
tracing_service_impl.cc: Producer 1 connected
tracing_service_impl.cc: Producer 1 registered data source "org.chromium.trace_event"
tracing_service_impl.cc: Producer 1 registered data source "org.chromium.trace_metadata"
...
tracing_service_impl.cc: Producer 2 connected
tracing_service_impl.cc: Producer 3 connected
tracing_service_impl.cc: Producer 2 registered data source "org.chromium.trace_event"
tracing_service_impl.cc: Producer 3 registered data source "org.chromium.trace_event"
tracing_service_impl.cc: Producer 4 connected
tracing_service_impl.cc: Producer 4 registered data source "org.chromium.trace_event"

Can this not be printed by default?