Don't bother layout until first navigation is done.

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

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index fa3e9134e84b79286012914bc05b8ff47bc49d5a..a308e3fd0803e0ecd966d13add0c4d98e8799ae3 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -1747,6 +1747,9 @@ void Document::updateLayoutTreeIfNeeded()
         return;
     }
 
+    if (m_frame && m_frame->isMainFrame() && isInitialEmptyDocument())
+        return;
+
     if (inStyleRecalc())
         return;
 
@@ -1999,6 +2002,9 @@ void Document::clearFocusedElementTimerFired(Timer<Document>*)
 // to instead suspend JavaScript execution.
 void Document::updateLayoutTreeIgnorePendingStylesheets()
 {
+    // TODO(kouhei): We need forced layout at this point. Bail out from skip layout tree path.
+    markNonInitialEmptyDocument();
+
     StyleEngine::IgnoringPendingStylesheet ignoring(styleEngine());
 
     if (styleEngine().hasPendingSheets()) {
@@ -2803,7 +2809,7 @@ void Document::dispatchUnloadEvents()
         return;
 
     // Don't remove event listeners from a transitional empty document (see https://bugs.webkit.org/show_bug.cgi?id=28716 for more information).
-    bool keepEventListeners = m_frame->loader().stateMachine()->isDisplayingInitialEmptyDocument() && m_frame->loader().provisionalDocumentLoader()
+    bool keepEventListeners = isInitialEmptyDocument() && m_frame->loader().provisionalDocumentLoader()
         && isSecureTransitionTo(m_frame->loader().provisionalDocumentLoader()->url());
     if (!keepEventListeners)
         removeAllEventListenersRecursively();
@@ -5510,6 +5516,20 @@ bool Document::hasActiveParser()
     return m_activeParserCount || (m_parser && m_parser->processingData());
 }
 
+bool Document::isInitialEmptyDocument() const
+{
+    return m_frame && m_frame->loader().stateMachine()->isDisplayingInitialEmptyDocument();
+}
+
+void Document::markNonInitialEmptyDocument()
+{
+    if (!m_frame)
+        return;
+    auto stateMachine = m_frame->loader().stateMachine();
+    if (stateMachine->isDisplayingInitialEmptyDocument())
+        stateMachine->advanceTo(FrameLoaderStateMachine::CommittedFirstRealLoad);
+}
+
 void Document::setContextFeatures(ContextFeatures& features)
 {
     m_contextFeatures = PassRefPtrWillBeRawPtr<ContextFeatures>(features);