Don't apply style elements or PIs with loading imports.

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 61 matching lines @@
     return toElement(node()).getAttribute(relAttr).contains("alternate");
 }
 
 bool StyleSheetCandidate::isEnabledViaScript() const
 {
     return isHTMLLink() && toHTMLLinkElement(node()).isEnabledViaScript();
 }
 
 bool StyleSheetCandidate::isEnabledAndLoading() const
 {
-    return isHTMLLink() && !toHTMLLinkElement(node()).isDisabled() && toHTMLLinkElement(node()).styleSheetIsLoading();
+    if (isHTMLLink())
+        return !toHTMLLinkElement(node()).isDisabled() && toHTMLLinkElement(node()).styleSheetIsLoading();
+
+    StyleSheet* sheet = this->sheet();

[esprehn, 2016/04/06 21:03:17]

hmm, can we not make this->sheet() and sheet->disabled() work for <link> ?

[rune, 2016/04/06 22:01:46]

Sheet is null while top-level css is loading for <link>. Relying on
this->sheet() to be non-null would change the behavior for setting the preferred
stylesheet via <link> title. Relying on sheet for load status of xml-stylesheet
is probably wrong for preferred stylesheet set via its title attribute. I don't
think we should try to fix that in this CL, though.

+    return sheet && !sheet->disabled() && sheet->isLoading();
 }
 
 bool StyleSheetCandidate::hasPreferrableName() const
 {
     ASSERT(isEnabledAndLoading() || sheet());
     return !isEnabledViaScript() && !title().isEmpty() && !isAlternate();
 }
 
 bool StyleSheetCandidate::canBeActivated(const String& currentPreferrableName) const
 {
@@ skipping 46 matching lines @@
         return toSVGStyleElement(node()).sheet();
     case Pi:
         return toProcessingInstruction(node()).sheet();
     }
 
     ASSERT_NOT_REACHED();
     return 0;
 }
 
 } // namespace blink