Make updateStyleAndLayoutTree ready for async stylesheet update.

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

Index: third_party/WebKit/Source/core/dom/StyleEngine.h
diff --git a/third_party/WebKit/Source/core/dom/StyleEngine.h b/third_party/WebKit/Source/core/dom/StyleEngine.h
index c3f47d518bb2967c88dc0a975c55b7c6441f08d5..208b0aa8d65d0fc8af37d73974c623e8f24cbd39 100644
--- a/third_party/WebKit/Source/core/dom/StyleEngine.h
+++ b/third_party/WebKit/Source/core/dom/StyleEngine.h
@@ -101,6 +101,7 @@ class CORE_EXPORT StyleEngine final
 
   const HeapVector<Member<CSSStyleSheet>> activeStyleSheetsForInspector() const;
 
+  bool needsActiveStyleUpdate() const;
   void setNeedsActiveStyleUpdate(StyleSheet*, StyleResolverUpdateMode);
   void addStyleSheetCandidateNode(Node&);
   void removeStyleSheetCandidateNode(Node&);
@@ -119,6 +120,7 @@ class CORE_EXPORT StyleEngine final
   void clearMediaQueryRuleSetStyleSheets();
   void updateStyleSheetsInImport(DocumentStyleSheetCollector& parentCollector);
   void updateActiveStyleSheets(StyleResolverUpdateMode);
+  void updateActiveStyle();
 
   enum ActiveSheetsUpdate { DontUpdateActiveSheets, UpdateActiveSheets };
   String preferredStylesheetSetName() const {
@@ -177,10 +179,10 @@ class CORE_EXPORT StyleEngine final
   void setRuleUsageTracker(StyleRuleUsageTracker*);
 
   StyleResolver& ensureResolver() {
+    updateActiveStyle();
     if (!m_resolver) {
       createResolver();
     } else if (m_resolver->hasPendingAuthorStyleSheets()) {
-      viewportRulesChanged();
       m_resolver->appendPendingAuthorStyleSheets();
       finishAppendAuthorStyleSheets();
     } else if (m_globalRuleSet.isDirty()) {
@@ -311,6 +313,9 @@ class CORE_EXPORT StyleEngine final
       const HeapVector<Member<RuleSet>>&);
   void invalidateSlottedElements(HTMLSlotElement&);
 
+  void updateViewport();
+  void updateActiveStyleSheets();
+
   Member<Document> m_document;
   bool m_isMaster;