Allow <link rel=stylesheet> in a connected shadow tree

third_party/WebKit/Source/core/dom/StyleSheetCandidate.cpp

 /*
  * Copyright (C) 2013 Google Inc. 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.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 70 matching lines @@
 {
     return isHTMLLink() && !toHTMLLinkElement(node()).isDisabled() && toHTMLLinkElement(node()).styleSheetIsLoading();
 }
 
 bool StyleSheetCandidate::canBeActivated(const String& currentPreferrableName) const
 {
     StyleSheet* sheet = this->sheet();
     if (!sheet || sheet->disabled() || !sheet->isCSSStyleSheet())
         return false;
 
-    if (sheet->ownerNode() && sheet->ownerNode()->isInShadowTree())
-        return true;
+    if (sheet->ownerNode() && sheet->ownerNode()->isInShadowTree()) {
+        if (isCSSStyle() || (isHTMLLink() && !isImport() && !isAlternate()))
+            return true;
+    }

[rune, 2016/08/01 09:22:15]

I think I would be leaning towards a behavior where the title attribute is
ignored, effectively making:

  <link rel="stylesheet" title="x">
  <link rel="alternate stylesheet" title="x">

behave as:

  <link rel="stylesheet"> // always enabled
  <link rel="alternate stylesheet"> // never enabled

With the current patch, the former behaves as:

  <link rel="alternate stylesheet" title="x">
  <link rel="alternate stylesheet" title="x">

Have you opened a spec issue?

 
     const AtomicString& title = this->title();
     if (!isEnabledViaScript() && !title.isEmpty() && title != currentPreferrableName)
         return false;
     if (isAlternate() && title.isEmpty())
         return false;
 
     return true;
 }
 
@@ skipping 30 matching lines @@
         return toSVGStyleElement(node()).sheet();
     case Pi:
         return toProcessingInstruction(node()).sheet();
     }
 
     ASSERT_NOT_REACHED();
     return 0;
 }
 
 } // namespace blink