Add ScopedGCCriticalSection to Trace::StopTracing.

This attempts to fix a deadlock in 545-tracing-and-jit with the read
barrier config. I think the cause is the same as what CL 174096
describes and it missed this one in Trace::StopTracing.

Bug: 26429931
Bug: 12687968
Change-Id: I02ca45e2667c9f6afc27d73919d6c31d204cc621
1 file changed