Closing register/upgrade timing hole primarily impacting IE

pkg/custom_element/lib/custom-elements.debug.js

 // Copyright (c) 2012 The Polymer Authors. All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //    * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //    * Redistributions in binary form must reproduce the above
 // copyright notice, this list of conditions and the following disclaimer
@@ skipping 1045 matching lines @@
     overrideAttributeApi(definition.prototype);
     // 7.1.5: Register the DEFINITION with DOCUMENT
     registerDefinition(name, definition);
     // 7.1.7. Run custom element constructor generation algorithm with PROTOTYPE
     // 7.1.8. Return the output of the previous step.
     definition.ctor = generateConstructor(definition);
     definition.ctor.prototype = definition.prototype;
     // force our .constructor to be our actual constructor
     definition.prototype.constructor = definition.ctor;
     // if initial parsing is complete
-    if (scope.ready) {
+    if (scope.ready || scope.performedInitialDocumentUpgrade) {
       // upgrade any pre-existing nodes of this type
       scope.upgradeAll(document);
     }
     return definition.ctor;
   }
 
   function ancestry(extnds) {
     var extendee = registry[extnds];
     if (extendee) {
       return ancestry(extendee.extends).concat([extendee]);
@@ skipping 301 matching lines @@
 
 })();
 (function(){
 
 // bootstrap parsing
 function bootstrap() {
   // parse document
   CustomElements.parser.parse(document);
   // one more pass before register is 'live'
   CustomElements.upgradeDocument(document);
+  CustomElements.performedInitialDocumentUpgrade = true;
   // choose async
   var async = window.Platform && Platform.endOfMicrotask ?
     Platform.endOfMicrotask :
     setTimeout;
   async(function() {
     // set internal 'ready' flag, now document.register will trigger
     // synchronous upgrades
     CustomElements.ready = true;
     // capture blunt profiling data
     CustomElements.readyTime = Date.now();
@@ skipping 61 matching lines @@
 
   // override
   fns.forEach(function(fn) {
     CustomElements[fn] = function(inNode) {
       return original[fn](ShadowDOMPolyfill.wrapIfNeeded(inNode));
     };
   });
 }
 
 })();