fix spelling in core libraries

sdk/lib/io/platform_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.
 
 part of dart.io;
 
 class _Platform {
   external static int _numberOfProcessors();
   external static String _pathSeparator();
   external static String _operatingSystem();
   external static _localHostname();
   external static _executable();
   external static _resolvedExecutable();
 
   /**
    * Retrieve the entries of the process environment.
    *
    * The result is an [Iterable] of strings, where each string represents
    * an environment entry.
    *
    * Environment entries should be strings containing
    * a non-empty name and a value separated by a '=' character.
    * The name does not contain a '=' character,
    * so the name is everything up to the first '=' character.
-   * Values are everything after the first '=' charcacter.
+   * Values are everything after the first '=' character.
    * A value may contain further '=' characters, and it may be empty.
    *
    * Returns an [OSError] if retrieving the environment fails.
    */
   external static _environment();
   external static List<String> _executableArguments();
   external static String _packageRoot();
   external static String _packageConfig();
   external static String _version();
 
   static String executable = _executable();
   static String resolvedExecutable = _resolvedExecutable();
   static String packageRoot = _packageRoot();
   static String packageConfig = _packageConfig();
 
-  // Cache the OS environemnt. This can be an OSError instance if
+  // Cache the OS environment. This can be an OSError instance if
   // retrieving the environment failed.
   static var/*OSError|Map<String,String>*/ _environmentCache;
 
   static int get numberOfProcessors => _numberOfProcessors();
   static String get pathSeparator => _pathSeparator();
   static String get operatingSystem => _operatingSystem();
   static Uri script;
 
   static String get localHostname {
     var result = _localHostname();
@@ skipping 66 matching lines @@
   V remove(Object key) => key is String ? _map.remove(key.toUpperCase()) : null;
   void clear() { _map.clear(); }
   void forEach(void f(String key, V value)) { _map.forEach(f); }
   Iterable<String> get keys => _map.keys;
   Iterable<V> get values => _map.values;
   int get length => _map.length;
   bool get isEmpty => _map.isEmpty;
   bool get isNotEmpty => _map.isNotEmpty;
   String toString() => _map.toString();
 }