Check if tracing is on before generating strings

Guard Trace.beginSection to avoid unnecessary StringBuilder usage, which
would result in GC garbage churn.

Also, convert sections to instants when that is more applicable. This
also guards against potential run-time crashes if the trace section
string is longer than 127 characters.

Finally, correct some tracing usage in try blocks.

Test: manual
Bug: 257075630
Change-Id: Ibe6f194c779256615a7887931256324f7c78811a