Add resource tests.

tests/corelib/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;
+}