Clean VM thread shutdown:

runtime/bin/run_vm_tests.cc

Index: runtime/bin/run_vm_tests.cc
diff --git a/runtime/bin/run_vm_tests.cc b/runtime/bin/run_vm_tests.cc
index 388006256ea8210ce3eae59a37365ac4729020f4..cb5899ec3f9bfad6e3b352cef96421a1ac69c05b 100644
--- a/runtime/bin/run_vm_tests.cc
+++ b/runtime/bin/run_vm_tests.cc
@@ -113,6 +113,10 @@ static int Main(int argc, const char** argv) {
   TestCaseBase::RunAll();
   // Apply the filter to all registered benchmarks.
   Benchmark::RunAll(argv[0]);
+
+  err_msg = Dart::Cleanup();
+  ASSERT(err_msg == NULL);
+
   // Print a warning message if no tests or benchmarks were matched.
   if (run_matches == 0) {
     fprintf(stderr, "No tests matched: %s\n", run_filter);