Setting the link title may change the preferred set.

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

Index: third_party/WebKit/Source/core/dom/StyleEngine.cpp
diff --git a/third_party/WebKit/Source/core/dom/StyleEngine.cpp b/third_party/WebKit/Source/core/dom/StyleEngine.cpp
index 8b7bd5459c5c6130a21fa736a63be342d6a2ff45..27d057c84bcec276de4309c6b02fde7fa4e94a55 100644
--- a/third_party/WebKit/Source/core/dom/StyleEngine.cpp
+++ b/third_party/WebKit/Source/core/dom/StyleEngine.cpp
@@ -531,7 +531,7 @@ CSSStyleSheet* StyleEngine::createSheet(Element* e, const String& text, TextPosi
     DCHECK(styleSheet);
     if (!e->isInShadowTree()) {
         styleSheet->setTitle(e->title());
-        setPreferredStylesheetSetNameIfNotSet(e->title());
+        setPreferredStylesheetSetNameIfNotSet(e->title(), DontUpdateActiveSheets);
     }
     return styleSheet;
 }
@@ -759,7 +759,7 @@ void StyleEngine::setStatsEnabled(bool enabled)
         m_styleResolverStats->reset();
 }
 
-void StyleEngine::setPreferredStylesheetSetNameIfNotSet(const String& name)
+void StyleEngine::setPreferredStylesheetSetNameIfNotSet(const String& name, ActiveSheetsUpdate activeSheetsUpdate)
 {
     if (!m_preferredStylesheetSetName.isEmpty())
         return;
@@ -768,10 +768,16 @@ void StyleEngine::setPreferredStylesheetSetNameIfNotSet(const String& name)
     // 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)
@@ -786,9 +792,7 @@ void StyleEngine::setSelectedStylesheetSetName(const String& name)
 
 void StyleEngine::setHttpDefaultStyle(const String& content)
 {
-    setPreferredStylesheetSetNameIfNotSet(content);
-    markDocumentDirty();
-    resolverChanged(FullStyleUpdate);
+    setPreferredStylesheetSetNameIfNotSet(content, UpdateActiveSheets);
 }
 
 void StyleEngine::ensureFullscreenUAStyle()