Clear MatchedPropertiesCache on StyleRule changes.

third_party/WebKit/Source/core/css/CSSStyleSheet.cpp

Index: third_party/WebKit/Source/core/css/CSSStyleSheet.cpp
diff --git a/third_party/WebKit/Source/core/css/CSSStyleSheet.cpp b/third_party/WebKit/Source/core/css/CSSStyleSheet.cpp
index 4420191583105b1419b10ff90c9ec831b8daf517..c7ddcfa2f93aa39ffb5f0ac3a01d505b64fc4d62 100644
--- a/third_party/WebKit/Source/core/css/CSSStyleSheet.cpp
+++ b/third_party/WebKit/Source/core/css/CSSStyleSheet.cpp
@@ -160,7 +160,14 @@ void CSSStyleSheet::didMutateRules() {
   DCHECK(m_contents->isMutable());
   DCHECK_LE(m_contents->clientSize(), 1u);
 
-  didMutate();
+  Document* owner = ownerDocument();
+  if (!owner)
+    return;
+  if (ownerNode() && ownerNode()->isConnected()) {
+    owner->styleEngine().setNeedsActiveStyleUpdate(ownerNode()->treeScope());
+    if (StyleResolver* resolver = owner->styleEngine().resolver())
+      resolver->invalidateMatchedPropertiesCache();
+  }
 }
 
 void CSSStyleSheet::didMutate() {