Make ShadowRoot stylesheet list work only when the shadow root is con…

…nected.

This avoids the issue of triggering stylesheet loads for disconnected stuff and
such, and is more consistent with Chrome and WebKit.

This is per the recent CSSWG resolution at
w3c/csswg-drafts#3096.

Differential Revision: https://phabricator.services.mozilla.com/D5699

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1490791
gecko-commit: 71f86120ca35d113a2462b2ffe68bc5accc813e4
gecko-integration-branch: autoland
gecko-reviewers: smaug

shadow-dom/ShadowRoot-interface.html

@@ -94,8 +94,10 @@
         var host = document.createElement('div');
         var shadowRoot = host.attachShadow({'mode': mode});
 
-        assert_equals(shadowRoot.styleSheets.length, 0, 'shadowRoot.styleSheets must be empty when the shadow root does not contain any stylesheets');
         shadowRoot.innerHTML = '<span></span><style> a.rule {} </style><style> b.rule {} </style>';
+        assert_equals(shadowRoot.styleSheets.length, 0, 'shadowRoot.styleSheets must be empty when the shadow root is not connected');
+
+        document.body.appendChild(host);
         assert_equals(shadowRoot.styleSheets.length, 2, 'shadowRoot.styleSheets must contain two items when the shadow root has two style elements');
         var styles = shadowRoot.querySelectorAll('style');
         assert_equals(shadowRoot.styleSheets[0], styles[0].sheet, 'shadowRoot.styleSheets[0] must be the first style element in the shadow root');

shadow-dom/untriaged/styles/test-003.html

@@ -46,9 +46,6 @@
     assert_equals(s.styleSheets.length, 0, 'There should be no style sheets');
 }), 'A_06_00_03_T02');
 
-//TODO Now this tests produces an error on Chromium because styleSheets.length
-//returns 0 when the shadow root is orphaned.
-//Tracking bug: http://crbug.com/392771
 test(unit(function (ctx) {
     var d = newRenderedHTMLDocument(ctx);
     var host = d.createElement('div');
@@ -60,8 +57,7 @@
     style.textContent = 'div {width: 50%;}';
     s.appendChild(style);
 
-    // The following line fixes the issue on Chromium, http://crbug.com/392771
-    // d.body.appendChild(host);
+    d.body.appendChild(host);
     assert_equals(s.styleSheets.length, 1, 'Style sheet is not accessible via styleSheets');
 }), 'A_06_00_03_T03');
 </script>