Remove spawnDomFunction from dart:html

sdk/lib/_internal/lib/isolate_helper.dart

Index: sdk/lib/_internal/lib/isolate_helper.dart
diff --git a/sdk/lib/_internal/lib/isolate_helper.dart b/sdk/lib/_internal/lib/isolate_helper.dart
index d8fcff4ad29d0eb0e027368b1c361ae4769a2a82..7a6e620372d45025e6e4497f2f2be1347d6c9a4c 100644
--- a/sdk/lib/_internal/lib/isolate_helper.dart
+++ b/sdk/lib/_internal/lib/isolate_helper.dart
@@ -604,15 +604,6 @@ class IsolateNatives {
     return spawn(name, null, false);
   }
 
-  static SendPort spawnDomFunction(void topLevelFunction()) {
-    final name = _getJSFunctionName(topLevelFunction);
-    if (name == null) {
-      throw new UnsupportedError(
-          "only top-level functions can be spawned.");
-    }
-    return spawn(name, null, true);
-  }
-
   // TODO(sigmund): clean up above, after we make the new API the default:
 
   static spawn(String functionName, String uri, bool isLight) {