Setting the link title may change the preferred set.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 515 matching lines @@
         DCHECK(contents);
         DCHECK(contents->isCacheableForStyleElement());
         DCHECK(contents->hasSingleOwnerDocument());
         contents->setIsUsedFromTextCache();
         styleSheet = CSSStyleSheet::createInline(contents, e, startPosition);
     }
 
     DCHECK(styleSheet);
     if (!e->isInShadowTree()) {
         styleSheet->setTitle(e->title());
-        setPreferredStylesheetSetNameIfNotSet(e->title());
+        setPreferredStylesheetSetNameIfNotSet(e->title(), DontUpdateActiveSheets);
     }
     return styleSheet;
 }
 
 CSSStyleSheet* StyleEngine::parseSheet(Element* e, const String& text, TextPosition startPosition)
 {
     CSSStyleSheet* styleSheet = nullptr;
     styleSheet = CSSStyleSheet::createInline(e, KURL(), startPosition, e->document().characterSet());
     styleSheet->contents()->parseStringAtPosition(text, startPosition);
     return styleSheet;
@@ skipping 207 matching lines @@
     if (!enabled) {
         m_styleResolverStats = nullptr;
         return;
     }
     if (!m_styleResolverStats)
         m_styleResolverStats = StyleResolverStats::create();
     else
         m_styleResolverStats->reset();
 }
 
-void StyleEngine::setPreferredStylesheetSetNameIfNotSet(const String& name)
+void StyleEngine::setPreferredStylesheetSetNameIfNotSet(const String& name, ActiveSheetsUpdate activeSheetsUpdate)
 {
     if (!m_preferredStylesheetSetName.isEmpty())
         return;
     m_preferredStylesheetSetName = name;
     // TODO(rune@opera.com): Setting the selected set here is wrong if the set
     // has been previously set by through Document.selectedStylesheetSet. Our
     // current implementation ignores the effect of Document.selectedStylesheetSet
     // and either only collects persistent style, or additionally preferred
-    // style when present. We are currently not marking the document scope dirty
-    // because preferred style is updated during active stylesheet update which
-    // would make this method re-entrant. Will need to change for async update.
+    // style when present.
     m_selectedStylesheetSetName = name;
+
+    // TODO(rune@opera.com): For async stylesheet update, we should always mark
+    // the TreeScope dirty here, and the synchronous active stylesheet update
+    // (resolverChanged) should go away.
+    if (activeSheetsUpdate == UpdateActiveSheets) {
+        markDocumentDirty();
+        resolverChanged(AnalyzedStyleUpdate);
+    }
 }
 
 void StyleEngine::setSelectedStylesheetSetName(const String& name)
 {
     m_selectedStylesheetSetName = name;
     // TODO(rune@opera.com): Setting Document.selectedStylesheetSet currently
     // has no other effect than the ability to read back the set value using
     // the same api. If it did have an effect, we should have marked the
     // document scope dirty and triggered an update of the active stylesheets
     // from here.
 }
 
 void StyleEngine::setHttpDefaultStyle(const String& content)
 {
-    setPreferredStylesheetSetNameIfNotSet(content);
-    markDocumentDirty();
-    resolverChanged(FullStyleUpdate);
+    setPreferredStylesheetSetNameIfNotSet(content, UpdateActiveSheets);
 }
 
 void StyleEngine::ensureFullscreenUAStyle()
 {
     CSSDefaultStyleSheets::instance().ensureDefaultStyleSheetForFullscreen();
     if (!m_resolver)
         return;
     if (!m_resolver->hasFullscreenUAStyle())
         m_resolver->resetRuleFeatures();
 }
@@ skipping 28 matching lines @@
 
 DEFINE_TRACE_WRAPPERS(StyleEngine)
 {
     for (auto sheet : m_injectedAuthorStyleSheets) {
         visitor->traceWrappers(sheet);
     }
     visitor->traceWrappers(m_documentStyleSheetCollection);
 }
 
 } // namespace blink