Fix some minor static type issues in dart:io implementation.

runtime/bin/file_impl.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.
 
 class _FileInputStream extends _BaseDataInputStream implements InputStream {
   _FileInputStream(String name) {
     _file = new File(name);
     _data = [];
     _position = 0;
     _file.onError = (e) {
@@ skipping 471 matching lines @@
     request[2] = mode._mode;  // Direct int value for serialization.
     _fileService.call(request).then((response) {
       if (_isErrorResponse(response)) {
         _reportError(response, "Cannot open file");
       } else {
         callback(new _RandomAccessFile(response, _name));
       }
     });
   }
 
-  RandomAccessFile openSync([FileMode mode = FileMode.READ]) {
+  RandomAccessFile openSync(FileMode mode) {

[Bill Hesse, 2012/03/14 15:32:42]

Removed.

The openSync() method is called with no arguments at about 30 spots, scattered
throughout the Dart code base.  These must all be changed, if we make the mode
argument non-optional.  This should be done in a separate change, if at all.

     if (_asyncUsed) {
       throw new FileIOException(
           "Mixed use of synchronous and asynchronous API");
     }
     if (mode != FileMode.READ &&
         mode != FileMode.WRITE &&
         mode != FileMode.APPEND) {
       throw new FileIOException("Unknown file mode. Use FileMode.READ, " +
                                 "FileMode.WRITE or FileMode.APPEND.");
     }
@@ skipping 62 matching lines @@
         _onError("Failed to read file");
       }
     };
   }
 
   List<int> readAsBytesSync() {
     if (_asyncUsed) {
       throw new FileIOException(
           "Mixed use of synchronous and asynchronous API");
     }
-    var opened = openSync();
+    var opened = openSync(FileMode.READ);
     var length = opened.lengthSync();
     var result = new ByteArray(length);
     var read = opened.readListSync(result, 0, length);
     if (read != length) {
       throw new FileIOException("Failed to read file");
     }
     opened.closeSync();
     return result;
   }
 
@@ skipping 62 matching lines @@
           "Mixed use of synchronous and asynchronous API");
     }
     var decoder = _StringDecoders.decoder(encoding);
     List<int> bytes = readAsBytesSync();
     decoder.write(bytes);
     return _getDecodedLines(decoder);
   }
 
   String get name() => _name;
 
-  void set onError(void handler(String error)) {
+  void set onError(void handler(Exception error)) {
     _onError = handler;
   }
 
   void _ensureFileService() {
     if (_fileService == null) {
       _fileService = _FileUtils.newServicePort();
     }
   }
 
   bool _isErrorResponse(response) {
@@ skipping 429 matching lines @@
   bool _asyncUsed;
   int _pendingWrites = 0;
 
   SendPort _fileService;
 
   Timer _noPendingWriteTimer;
 
   Function _onNoPendingWrites;
   Function _onError;
 }