Ensure that dom-bind always waits until DOMContentLoaded to render. T…

…his ensures a script can install api on the dom-bind prior to it rendering. Previously dom-bind waited for first render, but an early parser yield can make this occur unexpectedly early.

src/lib/template/dom-bind.html

@@ -69,7 +69,13 @@
       // have resolved
       var self = this;
       Polymer.RenderStatus.whenReady(function() {
-        self._markImportsReady();
+        if (document.readyState == 'loading') {
+          document.addEventListener('DOMContentLoaded', function() {
+            self._markImportsReady(); 
+          });
+        } else {  
+          self._markImportsReady();
+        }
       });
     },