Fix Isolate scopes in service isolate shutdown

runtime/vm/service_isolate.cc

Index: runtime/vm/service_isolate.cc
diff --git a/runtime/vm/service_isolate.cc b/runtime/vm/service_isolate.cc
index a2156e45305ddfcf699b5be84d95b087b266114e..5bcd7cb6ee8ef80a9203ce3df36ab13f6cff4b2b 100644
--- a/runtime/vm/service_isolate.cc
+++ b/runtime/vm/service_isolate.cc
@@ -359,8 +359,10 @@ class RunServiceTask : public ThreadPool::Task {
         OS::PrintErr("vm-service: Error: %s\n", error.ToErrorCString());
       }
       Dart::RunShutdownCallback();
-
+    }
+    {
       // Shut the isolate down.
+      SwitchIsolateScope switch_scope(I);
       Dart::ShutdownIsolate();
     }

[siva, 2015/10/30 15:22:47]

Can we switch this to:

{
   ASSERT(Isolate::Current() == NULL);
   StartIsolateScope start_scope(I);
   {
      Thread* T ...
      .....
      .....
   }
   Dart::ShutdownIsolate();
}

StartIsolateScope itself works fine if the isolate is shutdown under it as there
is a check in Thread::ExitIsolate.

I would like to minimize usage of SwitchIsolateScope in the VM code as far as
possible.

[zra, 2015/10/30 16:48:40]

Discussed offline. It is also not possible to do ShutdownIsolate inside of a
StartIsolateScope.

     if (FLAG_trace_service) {