Fix file test to test for both decomposed and precomposed utf16

tests/standalone/standalone.status

 # 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.
 
 out_of_memory_test: Skip # Issue 2345
 
 package/invalid_uri_test: Fail, OK # Fails intentionally
 
 [ $runtime == vm ]
 io/directory_non_ascii_test: Fail  # Posting non-ascii strings through ports.
@@ skipping 12 matching lines @@
 
 [ $runtime == vm && $system == linux ]
 io/test_runner_test: Pass, Fail  # Issue 1947
 
 [ $runtime == vm && $system == macos ]
 # This test fails with "Too many open files" on the Mac OS buildbot.
 # This is expected as MacOS by default runs with a very low number
 # of allowed open files ('ulimit -n' says something like 256).
 io/socket_many_connections_test: Skip
 
-io/file_non_ascii_sync_test: Fail  # issue 6702
-io/directory_non_ascii_sync_test: Fail  # issue 6702
-io/process_non_ascii_test: Fail  # issue 6702
-
 [ $runtime == vm && $system == windows ]
 io/file_system_links_test: Skip  # No links on Windows.
 
 [ $compiler == none && $runtime == drt ]
 io/*: Skip # Don't run tests using dart:io in the browser
 crypto/*: Skip # Don't run tests using dart:io in the browser
 package/*: Skip # Do not run those in Dartium.
 
 [ $compiler == dartc ]
 *: Skip
@@ skipping 30 matching lines @@
 [ $compiler == dart2js && $browser ]
 *: Skip
 
 [ $compiler == dart2js && $checked ]
 io/http_read_test: Skip # Timeout TODO(ngeoffray): investigate
 io/list_input_stream_test: Skip # Timeout TODO(ngeoffray): investigate
 
 [ $compiler == dart2dart ]
 # Skip until we stabilize language tests.
 *: Skip