[dart:io] Adds functions to set file access and modification time

sdk/lib/io/file.dart

Index: sdk/lib/io/file.dart
diff --git a/sdk/lib/io/file.dart b/sdk/lib/io/file.dart
index cb9cdcc8e80fbc45af9bd8d340d632d7b0a5ccee..7d4c97d5fcc40cb66b936513d3e3143a62bebe5f 100644
--- a/sdk/lib/io/file.dart
+++ b/sdk/lib/io/file.dart
@@ -310,14 +310,45 @@ abstract class File implements FileSystemEntity {
   File get absolute;
 
   /**
-   * Get the last-modified time of the file. Returns a
+   * Gets the last-accessed time of the file. Returns a
+   * [:Future<DateTime>:] that completes with a [DateTime] object for the
+   * access date.
+   */
+  Future<DateTime> lastAccessed();
+
+  /**
+   * Gets the last-accessed time of the file. Throws an exception
+   * if the file does not exist.
+   *
+   * Throws a [FileSystemException] if the operation fails.
+   */
+  DateTime lastAccessedSync();
+
+  /**
+   * Modifies the time the file was last accessed.
+   *
+   * Returns a [:Future<File>:] that completes with this
+   * [File] when the attributes have been set. If the access time
+   * cannot be set, the future completes with an exception.
+   */
+  Future<File> setLastAccessed(DateTime time);
+
+  /**
+   * Synchronously modifies the time the file was last accessed.
+   *
+   * If the attributes cannot be set, throws a [FileSystemException].
+   */
+  void setLastAccessedSync(DateTime time);
+
+  /**
+   * Gets the last-modified time of the file. Returns a
    * [:Future<DateTime>:] that completes with a [DateTime] object for the
    * modification date.
    */
   Future<DateTime> lastModified();
 
   /**
-   * Get the last-modified time of the file. Throws an exception
+   * Gets the last-modified time of the file. Throws an exception
    * if the file does not exist.
    *
    * Throws a [FileSystemException] if the operation fails.
@@ -325,6 +356,22 @@ abstract class File implements FileSystemEntity {
   DateTime lastModifiedSync();
 
   /**
+   * Modifies the time the file was last modified.
+   *
+   * Returns a [:Future<File>:] that completes with this
+   * [File] when the attributes have been set. If the modification
+   * time cannot be set, the future completes with an exception.
+   */
+  Future<File> setLastModified(DateTime time);
+
+  /**
+   * Synchronously modifies the time the file was last modified.
+   *
+   * If the attributes cannot be set, throws a [FileSystemException].
+   */
+  void setLastModifiedSync(DateTime time);
+
+  /**
    * Open the file for random access operations. Returns a
    * [:Future<RandomAccessFile>:] that completes with the opened
    * random access file. [RandomAccessFile]s must be closed using the