Don't bother layout until first navigation is done.

third_party/WebKit/Source/core/dom/Document.h

 /*
  * 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, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 947 matching lines @@
     void didLoadAllImports();
 
     void adjustFloatQuadsForScrollAndAbsoluteZoom(Vector<FloatQuad>&, LayoutObject&);
     void adjustFloatRectForScrollAndAbsoluteZoom(FloatRect&, LayoutObject&);
 
     bool hasActiveParser();
     unsigned activeParserCount() { return m_activeParserCount; }
     void incrementActiveParserCount() { ++m_activeParserCount; }
     void decrementActiveParserCount() { --m_activeParserCount; }
 
+    bool isInitialEmptyDocument() const;
+
     void setContextFeatures(ContextFeatures&);
     ContextFeatures& contextFeatures() const { return *m_contextFeatures; }
 
     ElementDataCache* elementDataCache() { return m_elementDataCache.get(); }
 
     void didLoadAllScriptBlockingResources();
     void didRemoveAllPendingStylesheet();
 
     bool inStyleRecalc() const { return m_lifecycle.state() == DocumentLifecycle::InStyleRecalc; }
 
@@ skipping 474 matching lines @@
 DEFINE_TYPE_CASTS(TreeScope, Document, document, true, true);
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 CORE_EXPORT void showLiveDocumentInstances();
 #endif
 
 #endif // Document_h