Let debug target pick the debugger port

runtime/bin/dbg_connection.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_DBG_CONNECTION_H_
 #define BIN_DBG_CONNECTION_H_
 
 #include "bin/builtin.h"
 #include "bin/utils.h"
 
@@ skipping 31 matching lines @@
 
   // Accessors.
   int debug_fd() const { return debug_fd_; }
 
   // Return message id of current debug command message.
   int MessageId();
 
   // Starts the native thread which listens for connections from
   // debugger clients, reads and dispatches debug command messages
   // from the client.
-  static void StartHandler(const char* address, int port_number);
+  static int StartHandler(const char* address, int port_number);
 
   // Called by Isolates when they need to wait for a connection
   // from debugger clients.
   static void WaitForConnection();
 
   // Sends a reply or an error message to a specific debugger client.
   static void SendMsg(int debug_fd, dart::TextBuffer* msg);
   static void SendError(int debug_fd, int msg_id, const char* err_msg);
 
   // Sends an event message to all debugger clients that are connected.
@@ skipping 42 matching lines @@
 
   friend class DebuggerConnectionImpl;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(DebuggerConnectionHandler);
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_DBG_CONNECTION_H_