Change imports to clean up irritating warning

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 afd3e210c910214d4612fa9ff8ff80b210d0b3a7..d87ca4f80d137b320e4353c1a6d38b7594ad2cd7 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -41285,11 +41285,11 @@ class Url extends DartHtmlDomObject implements UrlUtils {
       return _blink.BlinkURL.instance
           .createObjectURL_Callback_1_(blob_OR_source_OR_stream);
     }
-    if ((blob_OR_source_OR_stream is MediaStream)) {
+    if ((blob_OR_source_OR_stream is MediaSource)) {
       return _blink.BlinkURL.instance
           .createObjectURL_Callback_1_(blob_OR_source_OR_stream);
     }
-    if ((blob_OR_source_OR_stream is MediaSource)) {
+    if ((blob_OR_source_OR_stream is MediaStream)) {
       return _blink.BlinkURL.instance
           .createObjectURL_Callback_1_(blob_OR_source_OR_stream);
     }