Rename File.readAsText to File.readAsString. There is no Text type in Dart

tests/standalone/io/file_error_test.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.
 //
 // Dart test program for testing error handling in file I/O.
 
 #import("dart:io");
 #import("dart:isolate");
 
 Directory tempDir() {
@@ skipping 255 matching lines @@
 void testReadAsTextNonExistent() {
   Directory temp = tempDir();
   ReceivePort p = new ReceivePort();
   p.receive((x, y) {
     p.close();
     temp.deleteSync(recursive: true);
   });
   var file = new File("${temp.path}/nonExistentFile4");
 
   // Non-existing file should throw exception.
-  Expect.throws(() => file.readAsTextSync(),
+  Expect.throws(() => file.readAsStringSync(),
                 (e) => checkOpenNonExistentFileException(e));
 
-  var readAsTextFuture = file.readAsText(Encoding.ASCII);
-  readAsTextFuture.then((data) => Expect.fail("Unreachable code"));
-  readAsTextFuture.handleException((e) {
+  var readAsStringFuture = file.readAsString(Encoding.ASCII);
+  readAsStringFuture.then((data) => Expect.fail("Unreachable code"));
+  readAsStringFuture.handleException((e) {
     checkOpenNonExistentFileException(e);
     p.toSendPort().send(null);
     return true;
   });
 }
 
 testReadAsLinesNonExistent() {
   Directory temp = tempDir();
   ReceivePort p = new ReceivePort();
   p.receive((x, y) {
@@ skipping 218 matching lines @@
   testReadAsBytesNonExistent();
   testReadAsTextNonExistent();
   testReadAsLinesNonExistent();
   testWriteByteToReadOnlyFile();
   testWriteListToReadOnlyFile();
   testTruncateReadOnlyFile();
   testOperateOnClosedFile();
   testRepeatedlyCloseFile();
   testRepeatedlyCloseFileSync();
 }