Clean VM thread shutdown:

runtime/bin/process.cc

Index: runtime/bin/process.cc
diff --git a/runtime/bin/process.cc b/runtime/bin/process.cc
index 2c90c11cdbebc29c364aaea4675c86cfc5b14c30..c678dfc4c8b944498eaf0fb971c6ccd048981beb 100644
--- a/runtime/bin/process.cc
+++ b/runtime/bin/process.cc
@@ -4,6 +4,7 @@
 
 #include "bin/dartutils.h"
 #include "bin/io_buffer.h"
+#include "bin/log.h"
 #include "bin/platform.h"
 #include "bin/process.h"
 #include "bin/socket.h"
@@ -216,8 +217,13 @@ void FUNCTION_NAME(Process_Exit)(Dart_NativeArguments args) {
   int64_t status = 0;
   // Ignore result if passing invalid argument and just exit 0.
   DartUtils::GetInt64Value(Dart_GetNativeArgument(args, 0), &status);
-  Dart_ExitIsolate();
-  Dart_Cleanup();
+  Dart_ShutdownIsolate();
+  Process::TerminateExitCodeHandler();
+  char* error = Dart_Cleanup();
+  if (error != NULL) {
+    Log::PrintErr("VM cleanup failed: %s\n", error);
+    free(error);
+  }
   exit(static_cast<int>(status));
 }