Use utf-8 encoding for listing and error page, in http_server VirtualDirectory.

pkg/http_server/test/virtual_directory_test.dart

Index: pkg/http_server/test/virtual_directory_test.dart
diff --git a/pkg/http_server/test/virtual_directory_test.dart b/pkg/http_server/test/virtual_directory_test.dart
index 97c7332fb66e82107e8a941aadcae21a5c0fe0a5..9bc65cfb8e646af9b188664aa1ef1cb9071ca020 100644
--- a/pkg/http_server/test/virtual_directory_test.dart
+++ b/pkg/http_server/test/virtual_directory_test.dart
@@ -140,6 +140,28 @@ void main() {
           });
       });
 
+      testVirtualDir('non-ascii-dir', (dir) {
+        var virDir = new VirtualDirectory(dir.path);
+        new Directory('${dir.path}/æøå').createSync();
+        virDir.allowDirectoryListing = true;
+
+        return getAsString(virDir, '/')
+          .then((result) {
+            expect(result, contains('æøå'));
+          });
+      });
+
+      testVirtualDir('content-type', (dir) {
+        var virDir = new VirtualDirectory(dir.path);
+        virDir.allowDirectoryListing = true;
+
+        return getHeaders(virDir, '/')
+          .then((headers) {
+            var contentType = headers.contentType.toString();
+            expect(contentType, 'text/html; charset=utf-8');
+          });
+      });
+
       if (!Platform.isWindows) {
         testVirtualDir('recursive-link', (dir) {
           var link = new Link('${dir.path}/recursive')..createSync('.');