Bug 1490791 - Make ShadowRoot stylesheet list work only when the shad…

…ow root is connected. r=smaug

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

dom/base/nsStyleLinkElement.cpp

@@ -303,11 +303,6 @@ nsStyleLinkElement::DoUpdateStyleSheet(nsIDocument* aOldDocument,
     // unload the stylesheet.  We want to do this even if updates are
     // disabled, since otherwise a sheet with a stale linking element pointer
     // will be hanging around -- not good!
-    //
-    // TODO(emilio): We can reach this code with aOldShadowRoot ==
-    // thisContent->GetContainingShadowRoot(), when moving the shadow host
-    // around. We probably could optimize some of this stuff out, is it worth
-    // it?
     if (aOldShadowRoot) {
       aOldShadowRoot->RemoveSheet(mStyleSheet);
     } else {
@@ -317,8 +312,7 @@ nsStyleLinkElement::DoUpdateStyleSheet(nsIDocument* aOldDocument,
     SetStyleSheet(nullptr);
   }
 
-  nsIDocument* doc = thisContent->IsInShadowTree()
-    ? thisContent->OwnerDoc() : thisContent->GetUncomposedDoc();
+  nsIDocument* doc = thisContent->GetComposedDoc();
 
   // Loader could be null during unlink, see bug 1425866.
   if (!doc || !doc->CSSLoader() || !doc->CSSLoader()->GetEnabled()) {

testing/web-platform/tests/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');

testing/web-platform/tests/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>