Clean up dart:io exceptions.

sdk/lib/io/process.dart

 // Copyright (c) 2013, 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.
 
 part of dart.io;
 
 // TODO(ager): The only reason for this class is that we
 // cannot patch a top-level at this point.
 class _ProcessUtils {
   external static void _exit(int status);
@@ skipping 237 matching lines @@
   static const ProcessSignal SIGVTALRM = const ProcessSignal._signal(26);
   static const ProcessSignal SIGPROF = const ProcessSignal._signal(27);
   static const ProcessSignal SIGPOLL = const ProcessSignal._signal(29);
   static const ProcessSignal SIGSYS = const ProcessSignal._signal(31);
 
   const ProcessSignal._signal(int this._signalNumber);
   final int _signalNumber;
 }
 
 
-class ProcessException implements Exception {
+class ProcessException implements IOException {
   const ProcessException(String this.executable,
                          List<String> this.arguments,
                          [String this.message = "",
                           int this.errorCode = 0]);
   String toString() {
     var msg = (message == null) ? 'OS error code: $errorCode' : message;
     var args = arguments.join(' ');
     return "ProcessException: $msg\n  Command: $executable $args";
   }
 
@@ skipping 10 matching lines @@
   /**
    * Contains the system message for the process exception if any.
    */
   final String message;
 
   /**
    * Contains the OS error code for the process exception if any.
    */
   final int errorCode;
 }