Implemented File create API.

runtime/bin/file.dart

 // Copyright (c) 2011, 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.
 
 interface File factory _File {
   /**
    * Create a File object.
    */
   File(String name);
 
   /**
    * Check if the file exists. The [existsHandler] is called with the
    * result when the operation completes.
    */
   void exists();
 
   /**
    * Synchronously check if the file exists.
    */
   bool existsSync();
 
   /**
    * Create the file. The [createHandler] is called when the file has
    * been created. The errorHandler is called if the file cannot be
-   * created.
+   * created. Existing files are left untouched by create. Calling
+   * create on an existing file might fail if there are restrictive
+   * permissions on the file.
    */
   void create();
 
   /**
-   * Synchronously create the file.
+   * Synchronously create the file. Existing files are left untouched
+   * by create. Calling create on an existing file might fail if there
+   * are restrictive permissions on the file.
    */
   void createSync();
 
   /**
    * Open the file for random access operations. When the file is
    * opened the openHandler is called. Opened files must be closed
    * using the [close] method. By default writable is false.
    */
   void open([bool writable]);
 
@@ skipping 153 matching lines @@
 
 interface FileOutputStream extends OutputStream {
 }
 
 
 class FileIOException implements Exception {
   const FileIOException([String this.message = ""]);
   String toString() => "FileIOException: $message";
   final String message;
 }