Migrate test block 4 to Dart 2.0.

tests/corelib_strong/data_resource_test.dart

-// Copyright (c) 2015, 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.
-
-const sampleText = "Sample text file.";
-
-main() async {
-  var uriEncoded = sampleText.replaceAll(' ', '%20');
-  await testUri("data:application/dart;charset=utf-8,$uriEncoded");
-  // TODO: Support other data: URI formats too.
-  // See: https://github.com/dart-lang/sdk/issues/24030
-  // await testUri("data:text/plain;charset=utf-8,$uriEncoded");
-  var base64Encoded = "U2FtcGxlIHRleHQgZmlsZS4=";
-  // await testUri("data:application/dart;charset=utf-8;base64,$base64Encoded");
-  // await testUri("data:text/plain;charset=utf-8;base64,$base64Encoded");
-}
-
-testUri(uriText) async {
-  var resource = new Resource(uriText);
-
-  if (resource.uri != Uri.parse(uriText)) {
-    throw "uriText: Incorrect URI: ${resource.uri}";
-  }
-
-  var text = await resource.readAsString();
-  if (text != sampleText) {
-    throw "uriText: Incorrect reading of text file: $text";
-  }
-
-  var bytes = await resource.readAsBytes();
-  if (!compareBytes(bytes, sampleText.codeUnits)) {
-    throw "uriText: Incorrect reading of bytes: $bytes";
-  }
-
-  var streamBytes = [];
-  await for (var byteSlice in resource.openRead()) {
-    streamBytes.addAll(byteSlice);
-  }
-  if (!compareBytes(streamBytes, sampleText.codeUnits)) {
-    throw "uriText: Incorrect reading of bytes: $bytes";
-  }
-}
-
-/// Checks that [bytes] and [expectedBytes] have the same contents.
-bool compareBytes(bytes, expectedBytes) {
-  if (bytes.length != expectedBytes.length) return false;
-  for (int i = 0; i < expectedBytes.length; i++) {
-    if (bytes[i] != expectedBytes[i]) return false;
-  }
-  return true;
-}