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

vm/port.cc

 // Copyright (c) 2012, 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 "vm/port.h"
 
 #include "platform/utils.h"
 #include "vm/dart_api_impl.h"
 #include "vm/isolate.h"
 #include "vm/message_handler.h"
@@ skipping 212 matching lines @@
   if (index < 0) {
     // Port does not exist.
     return false;
   }
 
   MessageHandler* handler = map_[index].handler;
   return handler->IsCurrentIsolate();
 }
 
 
+Isolate* PortMap::GetIsolate(Dart_Port id) {
+  MutexLocker ml(mutex_);
+  intptr_t index = FindPort(id);
+  if (index < 0) {
+    // Port does not exist.
+    return NULL;
+  }
+
+  MessageHandler* handler = map_[index].handler;
+  return handler->GetIsolate();
+}
+
+
 void PortMap::InitOnce() {
   mutex_ = new Mutex();
 
   static const intptr_t kInitialCapacity = 8;
   // TODO(iposva): Verify whether we want to keep exponentially growing.
   ASSERT(Utils::IsPowerOfTwo(kInitialCapacity));
   map_ = new Entry[kInitialCapacity];
   memset(map_, 0, kInitialCapacity * sizeof(Entry));
   capacity_ = kInitialCapacity;
   used_ = 0;
   deleted_ = 0;
 }
 
 }  // namespace dart