Avoid synchronous stylesheet update on html import loaded.

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 6b7206772724c3bbbfce8c77bf4964bafec46250..a7197e7926d96ffc4586ab912b8233a9947aff7b 100644
--- a/third_party/WebKit/Source/core/dom/StyleEngine.h
+++ b/third_party/WebKit/Source/core/dom/StyleEngine.h
@@ -117,6 +117,9 @@ class CORE_EXPORT StyleEngine final
   RuleSet* WatchedSelectorsRuleSet() {
     return global_rule_set_.WatchedSelectorsRuleSet();
   }
+  bool HasStyleSheets() const {
+    return GetDocumentStyleSheetCollection().HasStyleSheets();
+  }
 
   RuleSet* RuleSetForSheet(CSSStyleSheet&);
   void MediaQueryAffectingValueChanged();