Don't bother layout until first navigation is done.

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 483 matching lines @@
         markDocumentDirty();
         return;
     }
 
     ASSERT(m_styleSheetCollectionMap.contains(&scope));
     m_dirtyTreeScopes.add(&scope);
 }
 
 void StyleEngine::markDocumentDirty()
 {
+    // Extension may inject CSS into about:blank document.
+    // Unblock layout in such case.
+    document().markNonInitialEmptyDocument();
+
     m_documentScopeDirty = true;
     if (document().importLoader())
         document().importsController()->master()->styleEngine().markDocumentDirty();
 }
 
 static bool isCacheableForStyleElement(const StyleSheetContents& contents)
 {
     // FIXME: Support copying import rules.
     if (!contents.importRules().isEmpty())
         return false;
@@ skipping 221 matching lines @@
     visitor->trace(m_dirtyTreeScopes);
     visitor->trace(m_activeTreeScopes);
     visitor->trace(m_fontSelector);
     visitor->trace(m_textToSheetCache);
     visitor->trace(m_sheetToTextCache);
 #endif
     CSSFontSelectorClient::trace(visitor);
 }
 
 } // namespace blink