Mark when we may have been invalidated to early out on repaintTreeAfterLayout.

Source/core/rendering/RenderObject.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/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 1494 matching lines @@
         return "repaint";
     case InvalidationRepaintRectangle:
         return "repaint rectangle";
     }
     ASSERT_NOT_REACHED();
     return "";
 }
 
 void RenderObject::repaintTreeAfterLayout()
 {
+    // If we didn't need invalidation then our children don't need as well.
+    // Skip walking down the tree as everything should be fine below us.
+    if (!mayNeedInvalidation())
+        return;
+
     clearRepaintState();
 
     for (RenderObject* child = firstChild(); child; child = child->nextSibling()) {
         if (!child->isOutOfFlowPositioned())

[fs, 2014/05/02 17:21:42]

Could the children be "gated" here instead? Won't matter much for non-wide trees
- and probably only micro-effect on wide trees (SVG DOMs are often wide.) It'll
boil down to the cost of the indirect (virtual) call. Just a note, and should
probably be backed up by numbers, so don't make too much of it - just
mentioning.

             child->repaintTreeAfterLayout();
     }
 }
 
 static PassRefPtr<JSONValue> jsonObjectForOldAndNewRects(const LayoutRect& oldRect, const LayoutRect& newRect)
 {
     RefPtr<JSONObject> object = JSONObject::create();
 
     object->setValue("old", jsonObjectForRect(oldRect));
     object->setValue("new", jsonObjectForRect(newRect));
@@ skipping 1862 matching lines @@
 {
     return objectIsRelayoutBoundary(this);
 }
 
 void RenderObject::clearRepaintState()
 {
     setShouldDoFullRepaintAfterLayout(false);
     setShouldDoFullRepaintIfSelfPaintingLayer(false);
     setShouldRepaintOverflow(false);
     setLayoutDidGetCalled(false);
+    setMayNeedInvalidation(false);
 }
 
 } // namespace WebCore
 
 #ifndef NDEBUG
 
 void showTree(const WebCore::RenderObject* object)
 {
     if (object)
         object->showTreeForThis();
@@ skipping 14 matching lines @@
 {
     if (object1) {
         const WebCore::RenderObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showRenderTreeAndMark(object1, "*", object2, "-", 0);
     }
 }
 
 #endif