Fixed Dictionary and Event hookup w/o --gen-interop

tools/dom/templates/html/impl/impl_MutationObserver.darttemplate

Index: tools/dom/templates/html/impl/impl_MutationObserver.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_MutationObserver.darttemplate b/tools/dom/templates/html/impl/impl_MutationObserver.darttemplate
index 3469eef1c0c86d14650a1dc3830710b1e4f4e0ba..d45e98a0e1c7b0e07fee7b6c73b57d9afb02febd 100644
--- a/tools/dom/templates/html/impl/impl_MutationObserver.darttemplate
+++ b/tools/dom/templates/html/impl/impl_MutationObserver.darttemplate
@@ -20,7 +20,7 @@ $endif
   }
 $if DARTIUM
   @DocsEditable()
-$if JSINTEROP
+  $if JSINTEROP
   static MutationObserver _create(callback) => wrap_jso(_blink.BlinkMutationObserver.instance.constructorCallback_1_((List<MutationRecord> mutations, MutationObserver observer) {
       var wrapped_mutations = [];
       for (var mutation in mutations) {
@@ -30,17 +30,9 @@ $if JSINTEROP
       // Wrap the MutationObserver too.
       callback(wrapped_mutations, wrap_jso(observer));
   }));
-$else
-  static MutationObserver _create(callback) => _blink.BlinkMutationObserver.instance.constructorCallback_1_((List<MutationRecord> mutations, MutationObserver observer) {
-      var wrapped_mutations = [];
-      for (var mutation in mutations) {
-        // Wrap the Javascript object for each MutationRecord.
-        wrapped_mutations.add(wrap_jso(mutation));
-      }
-      // Wrap the MutationObserver too.
-      callback(wrapped_mutations, wrap_jso(observer));
-  });
-$endif
+  $else
+  static MutationObserver _create(callback) => _blink.BlinkMutationObserver.instance.constructorCallback_1_(callback);
+  $endif
 $endif
 
   /**