Make updateStyleAndLayoutTree ready for async stylesheet update.

third_party/WebKit/Source/core/css/resolver/ViewportStyleResolver.cpp

 /*
  * Copyright (C) 2012-2013 Intel Corporation. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above
  *    copyright notice, this list of conditions and the following
  *    disclaimer.
@@ skipping 281 matching lines @@
   if (documentStyle->hasViewportUnits())
     m_hasViewportUnits = true;
   documentStyle->setHasViewportUnits(documentStyleHasViewportUnits);
 
   return result;
 }
 
 void ViewportStyleResolver::initialViewportChanged() {
   if (m_needsUpdate == CollectRules)
     return;
+  if (m_hasViewportUnits)
+    m_needsUpdate = Resolve;
 
   auto& results = m_viewportDependentMediaQueryResults;
   for (unsigned i = 0; i < results.size(); i++) {
     if (m_initialViewportMedium->eval(results[i]->expression()) !=
         results[i]->result()) {
       m_needsUpdate = CollectRules;
-      return;
+      break;
     }
   }
-  if (m_hasViewportUnits)
-    m_needsUpdate = Resolve;
+  if (m_needsUpdate == NoUpdate)
+    return;
+  m_document->scheduleLayoutTreeUpdateIfNeeded();
 }
 
 void ViewportStyleResolver::setNeedsCollectRules() {
   m_needsUpdate = CollectRules;
+  m_document->scheduleLayoutTreeUpdateIfNeeded();
 }
 
 void ViewportStyleResolver::updateViewport(
     DocumentStyleSheetCollection& collection) {
   if (m_needsUpdate == NoUpdate)
     return;
   if (m_needsUpdate == CollectRules) {
     reset();
     collectViewportRulesFromUASheets();
     if (RuntimeEnabledFeatures::cssViewportEnabled())
       collection.collectViewportRules(*this);
   }
   resolve();
   m_needsUpdate = NoUpdate;
 }
 
 DEFINE_TRACE(ViewportStyleResolver) {
   visitor->trace(m_document);
   visitor->trace(m_propertySet);
   visitor->trace(m_initialViewportMedium);
   visitor->trace(m_viewportDependentMediaQueryResults);
   visitor->trace(m_deviceDependentMediaQueryResults);
 }
 
 }  // namespace blink