StyleResolver should update RuleSets lazily.

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index 3388b1d232304afa36428ef56a5ff40e83fa8307..a3faa382a80c6e37d7aefb8404098eb69efa07de 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -616,6 +616,7 @@ MediaQueryMatcher& Document::mediaQueryMatcher()
 {
     if (!m_mediaQueryMatcher)
         m_mediaQueryMatcher = MediaQueryMatcher::create(this);
+    appendPendingStyleSheetsIfNeeded(m_styleResolver.get());
     return *m_mediaQueryMatcher;
 }
 
@@ -1704,6 +1705,8 @@ void Document::recalcStyle(StyleRecalcChange change)
     if (m_elemSheet && m_elemSheet->contents()->usesRemUnits())
         m_styleEngine->setUsesRemUnit(true);
 
+    appendPendingStyleSheetsIfNeeded(m_styleResolver.get());
+
     {
         PostAttachCallbacks::SuspendScope suspendPostAttachCallbacks;
         RenderWidget::UpdateSuspendScope suspendWidgetHierarchyUpdates;
@@ -1757,7 +1760,7 @@ void Document::recalcStyle(StyleRecalcChange change)
 
         if (m_styleResolver) {
             // Pseudo element removal and similar may only work with these flags still set. Reset them after the style recalc.
-            m_styleEngine->resetCSSFeatureFlags(m_styleResolver->ruleFeatureSet());
+            m_styleEngine->resetCSSFeatureFlags(m_styleResolver->ensureRuleFeatureSet());
             m_styleResolver->clearStyleSharingList();
         }
     }
@@ -1904,12 +1907,16 @@ PassRefPtr<RenderStyle> Document::styleForElementIgnoringPendingStylesheets(Elem
 {
     ASSERT_ARG(element, element->document() == this);
     TemporaryChange<bool> ignoreStyleSheets(m_ignorePendingStylesheets, true);
-    return styleResolver()->styleForElement(element, element->parentNode() ? element->parentNode()->computedStyle() : 0);
+    StyleResolver* resolver = styleResolver();
+    appendPendingStyleSheetsIfNeeded(resolver);
+    return resolver->styleForElement(element, element->parentNode() ? element->parentNode()->computedStyle() : 0);
 }
 
 PassRefPtr<RenderStyle> Document::styleForPage(int pageIndex)
 {
-    return styleResolver()->styleForPage(pageIndex);
+    StyleResolver* resolver = styleResolver();
+    appendPendingStyleSheetsIfNeeded(resolver);
+    return resolver->styleForPage(pageIndex);
 }
 
 bool Document::isPageBoxVisible(int pageIndex)
@@ -1974,7 +1981,7 @@ void Document::createStyleResolver()
     ASSERT(frame());
 
     m_styleResolver = adoptPtr(new StyleResolver(*this));
-    m_styleEngine->combineCSSFeatureFlags(m_styleResolver->ruleFeatureSet());
+    m_styleEngine->combineCSSFeatureFlags(m_styleResolver->ensureRuleFeatureSet());
 }
 
 void Document::clearStyleResolver()