Avoid always style recalc when removing 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 8d902cd52e21c44170e669d15f4a279d8e1a9cfc..25f033737f28e93a14dc0368016b6865301dddad 100644
--- a/Source/core/dom/StyleEngine.cpp
+++ b/Source/core/dom/StyleEngine.cpp
@@ -288,6 +288,25 @@ void StyleEngine::removePendingSheet(Node* styleSheetCandidateNode, RemovePendin
     m_document.didRemoveAllPendingStylesheet();
 }
 
+void StyleEngine::modifiedStyleSheet(StyleSheet* sheet)
+{
+    if (!sheet)
+        return;
+
+    Node* node = sheet->ownerNode();
+    if (!node || !node->inDocument())
+        return;
+
+    TreeScope& treeScope = isHTMLStyleElement(node) ? node->treeScope() : m_document;
+    ASSERT(isHTMLStyleElement(node) || treeScope == m_document);
+
+    if (treeScope == m_document) {
+        m_needsDocumentStyleSheetsUpdate = true;
+        return;
+    }
+    m_dirtyTreeScopes.add(&treeScope);
+}
+
 void StyleEngine::addStyleSheetCandidateNode(Node* node, bool createdByParser)
 {
     if (!node->inDocument())