Skip ruleset invalidations for SubtreeStyleChange roots.

third_party/WebKit/Source/core/dom/StyleEngine.cpp

Index: third_party/WebKit/Source/core/dom/StyleEngine.cpp
diff --git a/third_party/WebKit/Source/core/dom/StyleEngine.cpp b/third_party/WebKit/Source/core/dom/StyleEngine.cpp
index 779ffa005a34ed750ddd852fd2447eb0b28b1620..0de4d370c2af5743d772ebe7c7caf3c472557be8 100644
--- a/third_party/WebKit/Source/core/dom/StyleEngine.cpp
+++ b/third_party/WebKit/Source/core/dom/StyleEngine.cpp
@@ -1084,11 +1084,15 @@ void StyleEngine::applyRuleSetChanges(
   if (changedRuleFlags & KeyframesRules)
     ScopedStyleResolver::keyframesRulesAdded(treeScope);
 
+  Node& invalidationRoot =
+      ScopedStyleResolver::invalidationRootForTreeScope(treeScope);
+  if (invalidationRoot.getStyleChangeType() >= SubtreeStyleChange)
+    return;
+
   if (fontsChanged || (changedRuleFlags & FullRecalcRules)) {
-    ScopedStyleResolver::invalidationRootForTreeScope(treeScope)
-        .setNeedsStyleRecalc(SubtreeStyleChange,
-                             StyleChangeReasonForTracing::create(
-                                 StyleChangeReason::ActiveStylesheetsUpdate));
+    invalidationRoot.setNeedsStyleRecalc(
+        SubtreeStyleChange, StyleChangeReasonForTracing::create(
+                                StyleChangeReason::ActiveStylesheetsUpdate));
     return;
   }