1. Create a port when a debugger object is created for an isolate, use this

vm/port.h

 // 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.
 
 #ifndef VM_PORT_H_
 #define VM_PORT_H_
 
 #include "include/dart_api.h"
 #include "vm/allocation.h"
 #include "vm/globals.h"
@@ skipping 25 matching lines @@
 
   // Enqueues the message in the port with id. Returns false if the port is not
   // active any longer.
   //
   // Claims ownership of 'message'.
   static bool PostMessage(Message* message);
 
   // Returns whether a port is local to the current isolate.
   static bool IsLocalPort(Dart_Port id);
 
+  // Returns the owning Isolate for port 'id'.
+  static Isolate* GetIsolate(Dart_Port id);
+
   static void InitOnce();
 
  private:
   friend class dart::PortMapTestPeer;
 
   // Mapping between port numbers and handlers.
   //
   // Free entries have id == 0 and handler == NULL. Deleted entries
   // have id == 0 and handler == deleted_entry_.
   typedef struct {
@@ skipping 22 matching lines @@
   static intptr_t capacity_;
   static intptr_t used_;
   static intptr_t deleted_;
 
   static Dart_Port next_port_;
 };
 
 }  // namespace dart
 
 #endif  // VM_PORT_H_