Fix race discovered by Valgrind

runtime/vm/profiler_android.cc

Index: runtime/vm/profiler_android.cc
diff --git a/runtime/vm/profiler_android.cc b/runtime/vm/profiler_android.cc
index 5c351a3e80f1b5d4e0ea9d78e3b42caa400cc37f..f1d57043d573cfaa5d07936fd0be6c8232019c54 100644
--- a/runtime/vm/profiler_android.cc
+++ b/runtime/vm/profiler_android.cc
@@ -100,10 +100,10 @@ void ProfilerManager::ThreadMain(uword parameters) {
   if (FLAG_trace_profiled_isolates) {
     OS::Print("ProfilerManager Android ready.\n");
   }
-  thread_running_ = true;
   {
     // Signal to main thread we are ready.
     ScopedMonitor startup_lock(start_stop_monitor_);
+    thread_running_ = true;
     startup_lock.Notify();
   }
   ScopedMonitor lock(monitor_);
@@ -115,10 +115,10 @@ void ProfilerManager::ThreadMain(uword parameters) {
   if (FLAG_trace_profiled_isolates) {
     OS::Print("ProfilerManager Android exiting.\n");
   }
-  thread_running_ = false;
   {
     // Signal to main thread we are exiting.
     ScopedMonitor shutdown_lock(start_stop_monitor_);
+    thread_running_ = false;
     shutdown_lock.Notify();
   }
 }