Support percent encoded data URIs in the standalone embedder.

runtime/tests/vm/dart/data_uri_failures_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.
+
+// Wrong MIME.
+import 'data:text/plain;charset=utf-8,foo%28%29%20%3D%3E%2042%3B';  /// 01: runtime error
+
+// No MIME.
+import 'data:;charset=utf-8,foo%28%29%20%3D%3E%2042%3B';  /// 02: runtime error
+
+// Wrong charset.
+import 'data:application/dart;charset=utf-16,foo%28%29%20%3D%3E%2042%3B';  /// 03: runtime error
+
+// No charset.
+import 'data:application/dart,foo%28%29%20%3D%3E%2042%3B';  /// 04: runtime error
+
+// Bad encoding.
+import 'data:application/dart;charset=utf-8,foo?%9g';  /// 05: runtime error
+
+// Wrong encoding.
+import 'data:application/dart;charset=utf-8;base64,Zm9vKCkgPT4gNDI7';  /// 06: runtime error
+
+main() {
+}