Support wedging isolates before startup or before exit.

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index 24ed4f57631a4135252ceb799bf7285bec95470e..6743b33cbd2d0a500eb87f6c28d355cce9104db0 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -142,12 +142,6 @@ 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.
@@ -486,7 +480,6 @@ 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_;