Fixed checked mode error for resolvePackageUri.

sdk/lib/_blink/dartium/_blink_dartium.dart

Index: sdk/lib/_blink/dartium/_blink_dartium.dart
diff --git a/sdk/lib/_blink/dartium/_blink_dartium.dart b/sdk/lib/_blink/dartium/_blink_dartium.dart
index a0fce4b249cd5e202bed23b9540030c09f86b051..eb77a675f777b5d905e8846736d73bb1f0a15093 100644
--- a/sdk/lib/_blink/dartium/_blink_dartium.dart
+++ b/sdk/lib/_blink/dartium/_blink_dartium.dart
@@ -7,6 +7,7 @@
  */
 library dart.dom._blink;
 
+import 'dart:async';
 import 'dart:js' as js;
 import 'dart:html' show DomException;
 import 'dart:_internal' as internal;
@@ -23278,8 +23279,11 @@ class Blink_Utils {
 
   // Below code sets up VMLibraryHooks for resolvePackageUri.
   static Uri resolvePackageUri(Uri packageUri) native "Utils_resolvePackageUri";
+  static Future<Uri> _resolvePackageUriFuture(Uri packageUri) async {
+      return resolvePackageUri(packageUri);
+  }
   static void _setupHooks() {
-    internal.VMLibraryHooks.resolvePackageUriFuture = resolvePackageUri;
+    internal.VMLibraryHooks.resolvePackageUriFuture = _resolvePackageUriFuture;
   }
 
   // Defines an interceptor if there is an appropriate JavaScript prototype to define it on.