Early-out from the prepaint tree walk

third_party/WebKit/Source/core/layout/LayoutObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc.
  *               All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved.
  *               (http://www.torchmobile.com/)
@@ skipping 2716 matching lines @@
       m_bitfields.isScrollAnchorObject()) {
     // Clear the bit first so that anchor.clear() doesn't recurse into
     // findReferencingScrollAnchors.
     m_bitfields.setIsScrollAnchorObject(false);
     findReferencingScrollAnchors(this, Clear);
   }
 }
 
 void LayoutObject::setNeedsPaintPropertyUpdate() {
   m_bitfields.setNeedsPaintPropertyUpdate(true);
+  // |paintInvalidationParent()| is used to ensure we continue marking across

[chrishtr, 2016/12/01 02:36:34]

I don't think this comment is necessary.

+  // frame boundaries.
+  if (LayoutObject* ancestor = paintInvalidationParent())
+    ancestor->setDescendantNeedsPaintPropertyUpdate();
+}
 
-  // Mark all ancestors as having a descendant needing paint property updates.
+void LayoutObject::setDescendantNeedsPaintPropertyUpdate() {

[chrishtr, 2016/12/01 02:36:35]

*markAncestorChain* is how other bit-setting methods are named for other tree
walks, like layout and
descendant-dependent PaintLayer flags.

+  if (m_bitfields.descendantNeedsPaintPropertyUpdate())
+    return;
+  m_bitfields.setDescendantNeedsPaintPropertyUpdate(true);
+
   // |paintInvalidationParent()| is used to ensure we continue marking across
   // frame boundaries.
   LayoutObject* ancestor = paintInvalidationParent();
   while (ancestor && !ancestor->descendantNeedsPaintPropertyUpdate()) {
     ancestor->m_bitfields.setDescendantNeedsPaintPropertyUpdate(true);
     ancestor = ancestor->paintInvalidationParent();
   }
 }
 
 void LayoutObject::setAncestorsNeedPaintPropertyUpdateForMainThreadScrolling() {
@@ skipping 753 matching lines @@
     const blink::LayoutObject* root = object1;
     while (root->parent())
       root = root->parent();
     root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
   } else {
     WTFLogAlways("%s", "Cannot showLayoutTree. Root is (nil)");
   }
 }
 
 #endif