Fix to distingish Document from HtmlDocument on ie9

sdk/lib/_internal/lib/native_helper.dart

Index: sdk/lib/_internal/lib/native_helper.dart
diff --git a/sdk/lib/_internal/lib/native_helper.dart b/sdk/lib/_internal/lib/native_helper.dart
index 3ad8b6cafe9ccba4104f0ce099dbb5e2390e2645..03b0ef5ba4940d920ae716238974342ac0ff9593 100644
--- a/sdk/lib/_internal/lib/native_helper.dart
+++ b/sdk/lib/_internal/lib/native_helper.dart
@@ -532,8 +532,10 @@ function(hooks) {
     if (tag == "Document") {
       // IE calls both HTML and XML documents "Document", so we check for the
       // xmlVersion property, which is the empty string on HTML documents.
-      if (!!o.xmlVersion) return "Document";
-      return "HTMLDocument";
+      // Since both dart:html classes Document and HtmlDocument share the same
+      // type, we must patch the instances and not the prototype.
+      if (!!o.xmlVersion) return "!Document";
+      return "!HTMLDocument";
     }
     // Patches for types which report themselves as Objects.
     if (tag == "Object") {