added library-level description for dart:indexed_db

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index bd228d2f4934bc59f8a92e335578632d2ecdd7c3..5e7b1167716c4ff187a42671da7ded3e9f7f176d 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -26098,13 +26098,13 @@ class Url extends NativeFieldWrapperClass1 {
     if ((blob_OR_source_OR_stream is Blob || blob_OR_source_OR_stream == null)) {
       return _createObjectURL_1(blob_OR_source_OR_stream);
     }
-    if ((blob_OR_source_OR_stream is MediaStream || blob_OR_source_OR_stream == null)) {
+    if ((blob_OR_source_OR_stream is MediaSource || blob_OR_source_OR_stream == null)) {
       return _createObjectURL_2(blob_OR_source_OR_stream);
     }
-    if ((blob_OR_source_OR_stream is MediaSource || blob_OR_source_OR_stream == null)) {
+    if ((blob_OR_source_OR_stream is _WebKitMediaSource || blob_OR_source_OR_stream == null)) {
       return _createObjectURL_3(blob_OR_source_OR_stream);
     }
-    if ((blob_OR_source_OR_stream is _WebKitMediaSource || blob_OR_source_OR_stream == null)) {
+    if ((blob_OR_source_OR_stream is MediaStream || blob_OR_source_OR_stream == null)) {
       return _createObjectURL_4(blob_OR_source_OR_stream);
     }
     throw new ArgumentError("Incorrect number or type of arguments");