Don't use same value for socket() and handle(), as they are different concepts.

runtime/bin/eventhandler_win.h

 // 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.
 
 #ifndef BIN_EVENTHANDLER_WIN_H_
 #define BIN_EVENTHANDLER_WIN_H_
 
 #if !defined(BIN_EVENTHANDLER_H_)
 #error Do not include eventhandler_win.h directly; use eventhandler.h instead.
 #endif
@@ skipping 210 matching lines @@
 
   virtual void EnsureInitialized(
     EventHandlerImplementation* event_handler) = 0;
 
   HANDLE handle() { return handle_; }
   Dart_Port port() { return port_; }
 
   void Lock();
   void Unlock();
 
-  bool CreateCompletionPort(HANDLE completion_port);
+  virtual bool CreateCompletionPort(HANDLE completion_port);
 
   void Close();
   virtual void DoClose();
   virtual bool IsClosed() = 0;
 
   bool IsHandleClosed() const { return handle_ == INVALID_HANDLE_VALUE; }
 
   void SetPortAndMask(Dart_Port port, intptr_t mask) {
     port_ = port;
     mask_ = mask;
@@ skipping 112 matching lines @@
   void Stop();
 
  private:
   int events_;
   bool recursive_;
 };
 
 
 class SocketHandle : public Handle {
  public:
-  SOCKET socket() { return reinterpret_cast<SOCKET>(handle_); }
+  SOCKET socket() const { return socket_; }
+
+  bool CreateCompletionPort(HANDLE completion_port);
 
  protected:
-  explicit SocketHandle(SOCKET s) : Handle(reinterpret_cast<HANDLE>(s)) {}
+  explicit SocketHandle(SOCKET s)
+      : Handle(INVALID_HANDLE_VALUE),
+        socket_(s) {}
   SocketHandle(SOCKET s, Dart_Port port)
-      : Handle(reinterpret_cast<HANDLE>(s), port) {}
+      : Handle(INVALID_HANDLE_VALUE, port),
+        socket_(s) {}
 
   virtual void HandleIssueError();
+
+ private:
+  const SOCKET socket_;
 };
 
 
 // Information on listen sockets.
 class ListenSocket : public SocketHandle {
  public:
   explicit ListenSocket(SOCKET s) : SocketHandle(s),
                                     AcceptEx_(NULL),
                                     pending_accept_count_(0),
                                     accepted_head_(NULL),
@@ skipping 151 matching lines @@
 
   TimeoutQueue timeout_queue_;  // Time for next timeout.
   bool shutdown_;
   HANDLE completion_port_;
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_EVENTHANDLER_WIN_H_