fix spelling in core libraries

sdk/lib/io/stdio.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;
 
 const int _STDIO_HANDLE_TYPE_TERMINAL = 0;
 const int _STDIO_HANDLE_TYPE_PIPE = 1;
 const int _STDIO_HANDLE_TYPE_FILE = 2;
 const int _STDIO_HANDLE_TYPE_SOCKET = 3;
@@ skipping 33 matching lines @@
    *
    * The argument [encoding] can be used to changed how the input should be
    * decoded. Default is [SYSTEM_ENCODING].
    *
    * If [retainNewlines] is `false`, the returned String will not contain the
    * final newline. If `true`, the returned String will contain the line
    * terminator. Default is `false`.
    *
    * If end-of-file is reached after any bytes have been read from stdin,
    * that data is returned.
-   * Returns `null` if no bytes preceeded the end of input.
+   * Returns `null` if no bytes preceded the end of input.
    */
   String readLineSync({Encoding encoding: SYSTEM_ENCODING,
                        bool retainNewlines: false}) {
     const CR = 13;
     const LF = 10;
     final List<int> line = <int>[];
     // On Windows, if lineMode is disabled, only CR is received.
     bool crIsNewline = Platform.isWindows &&
         (stdioType(stdin) == StdioType.TERMINAL) &&
         !lineMode;
@@ skipping 14 matching lines @@
       while (true) {
         int byte = readByteSync();
         if (byte < 0) {
           if (line.isEmpty) return null;
           break;
         }
         if (byte == LF || byte == CR) break;
         line.add(byte);
       }
     } else {
-      // Case having to hande CR LF as a single unretained line terminator.
+      // Case having to handel CR LF as a single unretained line terminator.
       outer: while (true) {
         int byte = readByteSync();
         if (byte == LF) break;
         if (byte == CR) {
           do {
             byte = readByteSync();
             if (byte == LF) break outer;
 
             line.add(CR);
           } while (byte == CR);
@@ skipping 265 matching lines @@
 }
 
 
 class _StdIOUtils {
   external static _getStdioOutputStream(int fd);
   external static Stdin _getStdioInputStream();
   /// Returns the socket type or `null` if [socket] is not a builtin socket.
   external static int _socketType(Socket socket);
   external static _getStdioHandleType(int fd);
 }