StyleResolver should update RuleSets lazily.

Source/core/css/MediaQueryMatcher.cpp

Index: Source/core/css/MediaQueryMatcher.cpp
diff --git a/Source/core/css/MediaQueryMatcher.cpp b/Source/core/css/MediaQueryMatcher.cpp
index 61fc729cdc7b9bf49fe15a6ecd2d53cd722f6206..55586ebd92c32a9263c0c9f1bc7d3414f42a3657 100644
--- a/Source/core/css/MediaQueryMatcher.cpp
+++ b/Source/core/css/MediaQueryMatcher.cpp
@@ -84,8 +84,8 @@ PassOwnPtr<MediaQueryEvaluator> MediaQueryMatcher::prepareEvaluator() const
         return nullptr;
 
     StyleResolver* styleResolver = m_document->styleResolver();
-    if (!styleResolver)
-        return nullptr;
+    ASSERT(styleResolver);
+    appendPendingStyleSheetsIfNeeded(styleResolver);
 
     RefPtr<RenderStyle> rootStyle = styleResolver->styleForElement(documentElement, 0 /*defaultParent*/, DisallowStyleSharing, MatchOnlyUserAgentRules);