Add missing Dart_ExitScope calls in some of the VM unit tests.

runtime/vm/custom_isolate_test.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 
 #include "vm/unit_test.h"
 
 // Custom Isolate Test.
@@ skipping 192 matching lines @@
   Dart_EnterIsolate(isolate());
   Dart_EnterScope();
 
   Dart_Handle result = Dart_HandleMessage();
   EXPECT_VALID(result);
 
   if (!Dart_HasLivePorts()) {
     OS::Print("<< Shutting down isolate(%p)\n", isolate());
     event_queue->RemoveEventsForIsolate(isolate());
     Dart_SetMessageNotifyCallback(NULL);
+    Dart_ExitIsolate();
     Dart_ShutdownIsolate();
   } else {
     Dart_ExitScope();
     Dart_ExitIsolate();
   }
   ASSERT(Dart_CurrentIsolate() == NULL);
 }
 
 
 static void NotifyMessage(Dart_Isolate dest_isolate) {
@@ skipping 127 matching lines @@
   }
   OS::Print("-- Finished event loop --\n");
   EXPECT_STREQ("Received: 43", saved_echo);
   free(saved_echo);
 
   delete event_queue;
   event_queue = NULL;
 }
 
 }  // namespace dart