Make Uri.base work in SkyView

sky/engine/bindings/builtin_natives.cc

Index: sky/engine/bindings/builtin_natives.cc
diff --git a/sky/engine/bindings/builtin_natives.cc b/sky/engine/bindings/builtin_natives.cc
index 022d781172d0bdc3c0f9cba1e047f685d8967cb9..f826ca828d07c9cd8298d52a31d5819d3021612f 100644
--- a/sky/engine/bindings/builtin_natives.cc
+++ b/sky/engine/bindings/builtin_natives.cc
@@ -192,9 +192,7 @@ void ScheduleMicrotask(Dart_NativeArguments args) {
 }
 
 void GetBaseURLString(Dart_NativeArguments args) {
-  String url;
-  if (Document* document = DOMDartState::CurrentDocument())
-    url = document->url().string();
+  String url = DOMDartState::Current()->url();
   Dart_SetReturnValue(args, StringToDart(DartState::Current(), url));
 }