Avoid the hash table StyleInvalidator::clearInvalidation in Node::detach when possible

Accessing the hash table in every ::detach call is a lot of overhead since
in the common case the Element is not even in the hash table. We should
check the needsStyleInvalidation() bit first.

Review URL: https://codereview.chromium.org/217423012

git-svn-id: svn://svn.chromium.org/blink/trunk@170539 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/css/invalidation/StyleInvalidator.cpp

@@ -41,10 +41,10 @@ StyleInvalidator::InvalidationList& StyleInvalidator::ensurePendingInvalidationL
 
 void StyleInvalidator::clearInvalidation(Node& node)
 {
+    if (node.isElementNode() && node.needsStyleInvalidation())
+        m_pendingInvalidationMap.remove(toElement(&node));
     node.clearChildNeedsStyleInvalidation();
     node.clearNeedsStyleInvalidation();
-    if (node.isElementNode())
-        m_pendingInvalidationMap.remove(toElement(&node));
 }
 
 void StyleInvalidator::clearPendingInvalidations()