Clean up dart:io exceptions.

sdk/lib/io/common.dart

 // 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.
 
 part of dart.io;
 
 // Constants used when working with native ports.
 // These must match the constants in runtime/bin/dartutils.h class CObject.
 const int _SUCCESS_RESPONSE = 0;
 const int _ILLEGAL_ARGUMENT_RESPONSE = 1;
@@ skipping 13 matching lines @@
  * Returns an Exception or an Error
  */
 _exceptionFromResponse(response, String message) {
   assert(_isErrorResponse(response));
   switch (response[_ERROR_RESPONSE_ERROR_TYPE]) {
     case _ILLEGAL_ARGUMENT_RESPONSE:
       return new ArgumentError();
     case _OSERROR_RESPONSE:
       var err = new OSError(response[_OSERROR_RESPONSE_MESSAGE],
                             response[_OSERROR_RESPONSE_ERROR_CODE]);
-      return new FileIOException(message, err);
+      return new FileException(message, err);
     case _FILE_CLOSED_RESPONSE:
-      return new FileIOException("File closed");
+      return new FileException("File closed");
     default:
       return new Exception("Unknown error");
   }
 }
 
 /**
+ * Base class for all IO related exceptions.
+ */
+abstract class IOException implements Exception {
+  String toString() => "IOException";
+}
+
+/**
   * An [OSError] object holds information about an error from the
   * operating system.
   */
-class OSError implements Error {
+class OSError {
   /** Constant used to indicate that no OS error code is available. */
   static const int noErrorCode = -1;
 
   /** Creates an OSError object from a message and an errorCode. */
   const OSError([String this.message = "", int this.errorCode = noErrorCode]);
 
   /** Converts an OSError object to a string representation. */
   String toString() {
     StringBuffer sb = new StringBuffer();
     sb.write("OS Error");
@@ skipping 72 matching lines @@
 class _BufferUtils {
   // Check if a List is a builtin VM List type. Returns true
   // if the List is a builtin VM List type and false if it is
   // a user defined List type.
   external static bool _isBuiltinList(List buffer);
 }
 
 class _IOCrypto {
   external static Uint8List getRandomBytes(int count);
 }