Merge pull request #138 from PolymerElements/insert-hidden-into-head-…

…of-doc

insert hidden globally

iron-flex-layout.html

@@ -58,9 +58,19 @@
 @pseudoElement iron-flex-layout
 @demo demo/index.html
 -->
+<script>
+  // This is left only for backward compatibility with projects
+  // that incorrectly relied on unscoped global [hidden] rules;
+  // removing would be a breaking change, but new projects
+  // should never rely on this.
+  (function() {
+    var style = document.createElement('style');
+    style.textContent = '[hidden] { display: none !important; }';
+    document.head.appendChild(style);
+  })();
+</script>
 <custom-style>
   <style is="custom-style">
-    /* IE 10 support for HTML5 hidden attr */
     [hidden] {
       display: none !important;
     }