Add File.copy(Sync) to dart:io.

sdk/lib/io/file.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;
 
 /**
  * FileMode describes the modes in which a file can be opened.
  */
 class FileMode {
@@ skipping 89 matching lines @@
    * Synchronously renames this file. Returns a [File]
    * instance for the renamed file.
    *
    * If [newPath] identifies an existing file, that file is
    * replaced. If [newPath] identifies an existing directory the
    * operation fails and an exception is thrown.
    */
   File renameSync(String newPath);
 
   /**
+   * Copy this file. Returns a `Future<File>` that completes
+   * with a [File] instance for the copied file.
+   *
+   * If [newPath] identifies an existing file, that file is
+   * replaced. If [newPath] identifies an existing directory, the
+   * operation fails and the future completes with an exception.
+   */
+  Future<File> copy(String newPath);
+
+   /**
+   * Synchronously copy this file. Returns a [File]
+   * instance for the copied file.
+   *
+   * If [newPath] identifies an existing file, that file is
+   * replaced. If [newPath] identifies an existing directory the
+   * operation fails and an exception is thrown.
+   */
+  File copySync(String newPath);
+
+  /**
    * Get the length of the file. Returns a [:Future<int>:] that
    * completes with the length in bytes.
    */
   Future<int> length();
 
   /**
    * Synchronously get the length of the file.
    *
    * Throws a [FileSystemException] if the operation fails.
    */
@@ skipping 441 matching lines @@
       }
     } else if (osError != null) {
       sb.write(": osError");
       if (path != null) {
         sb.write(", path = $path");
       }
     }
     return sb.toString();
   }
 }