Add flag to pin and service command to release isolates

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index e0ce7cb3900c1a52d96a136e2b0c5d38c76a7210..11ef015bea7cf913d83aaea618a2c58c1491d2f0 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -145,6 +145,12 @@ class Isolate : public BaseIsolate {
 
   int64_t start_time() const { return start_time_; }
 
+  // Creates the pin port (responsible for stopping the isolate from being
+  // destroyed).
+  void CreatePinPort();
+  // Closes pin port.
+  void ClosePinPort();
+
   Dart_Port main_port() { return main_port_; }
   void set_main_port(Dart_Port port) {
     ASSERT(main_port_ == 0);  // Only set main port once.
@@ -452,6 +458,7 @@ class Isolate : public BaseIsolate {
   Dart_MessageNotifyCallback message_notify_callback_;
   char* name_;
   int64_t start_time_;
+  Dart_Port pin_port_;
   Dart_Port main_port_;
   Heap* heap_;
   ObjectStore* object_store_;