listen for HTMLImportsLoaded only if HTMLImports.ready is false

Author: sorvell

src/boot.js

@@ -53,7 +53,8 @@ if (document.readyState === 'complete' || scope.flags.eager) {
 // When loading at other readyStates, wait for the appropriate DOM event to 
 // bootstrap.
 } else {
-  var loadEvent = window.HTMLImports ? 'HTMLImportsLoaded' : 'DOMContentLoaded';
+  var loadEvent = window.HTMLImports && !HTMLImports.ready ?
+      'HTMLImportsLoaded' : 'DOMContentLoaded';
   window.addEventListener(loadEvent, bootstrap);
 }