Defer style recalc when inserting extension stylesheets.

Source/core/dom/StyleEngine.cpp

Index: Source/core/dom/StyleEngine.cpp
diff --git a/Source/core/dom/StyleEngine.cpp b/Source/core/dom/StyleEngine.cpp
index 41e41f211d32bd840127f931a7b7eecfb4d9ae93..95affb95dcfc13cd03fbce03ee468d3b681973d5 100644
--- a/Source/core/dom/StyleEngine.cpp
+++ b/Source/core/dom/StyleEngine.cpp
@@ -231,7 +231,7 @@ void StyleEngine::invalidateInjectedStyleSheetCache()
 void StyleEngine::addAuthorSheet(PassRefPtrWillBeRawPtr<StyleSheetContents> authorSheet)
 {
     m_authorStyleSheets.append(CSSStyleSheet::create(authorSheet, m_document));
-    document().addedStyleSheet(m_authorStyleSheets.last().get(), RecalcStyleImmediately);
+    document().addedStyleSheet(m_authorStyleSheets.last().get(), RecalcStyleDeferred);
     markDocumentDirty();
 }