Add Resource class.

runtime/lib/core_patch.dart

Index: runtime/lib/core_patch.dart
diff --git a/runtime/lib/core_patch.dart b/runtime/lib/core_patch.dart
index 2a45ae708efed16d1b8b4276978c5a8cd8b28de5..0358cc28ddd79b8ecfe4959164b4572596cc7245 100644
--- a/runtime/lib/core_patch.dart
+++ b/runtime/lib/core_patch.dart
@@ -205,3 +205,27 @@ class _SyncIterator implements Iterator {
     }
   }
 }
+
+patch class Resource {
+  /* patch */ const factory Resource(String uri) = _Resource;
+}
+
+class _Resource implements Resource {
+  final String _location;
+
+  const _Resource(String uri) : _location = uri;
+
+  Uri get uri => Uri.base.resolve(_location);
+
+  Stream<List<int>> openRead() {
+    throw new UnimplementedError("openRead");
+  }
+
+  Future<List<int>> readAsBytes() {
+    throw new UnimplementedError("readAsBytes");
+  }
+
+  Future<String> readAsString({Encoding encoding}) {
+    throw new UnimplementedError("readAsString");
+  }
+}