fix analysis issue caught by dart2js bots

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

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of $LIBRARYNAME;
 
 /**
  * Lazy implementation of the child nodes of an element that does not request
  * the actual child nodes of an element until strictly necessary greatly
  * improving performance for the typical cases where it is not required.
@@ skipping 276 matching lines @@
   }
 
   /** Unbinds all bound attributes. */
   @Experimental
   void unbindAll() {
     TemplateElement.mdvPackage(this).unbindAll();
   }
 
   /** Gets the template instance that instantiated this node, if any. */
   @Experimental
-  TemplateInstance get templateInstance => mdvPackage(this).templateInstance;
+  TemplateInstance get templateInstance =>
+      TemplateElement.mdvPackage(this).templateInstance;
 
 $!MEMBERS
 }