[S.P.] Invalidate the document element for view background when needed

Source/core/layout/LayoutObject.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 238 matching lines @@
 
     void assertSubtreeClearedPaintInvalidationState() const
     {
         for (const LayoutObject* renderer = this; renderer; renderer = renderer->nextInPreOrder())
             renderer->assertRendererClearedPaintInvalidationState();
     }
 
 #endif
 
     // FIXME: This could be used when changing the size of a renderer without children to skip some invalidations.
-    bool rendererHasNoBoxEffect() const
+    // FIXME: This is incorrect for document element. Remove this when we enable slimming paint.
+    bool rendererHasNoBoxEffectObsolete() const
     {
         return !style()->hasVisualOverflowingEffect() && !style()->hasBorder() && !style()->hasBackground();
     }

[Xianzhu, 2015/03/18 22:44:19]

Because the current code works well, I don't want to bother change it (which
will cause many layout test expectation changes). I'd like to keep the above old
code and remove it when we remove all the old code.

 
+    // Correct version of !rendererHasNoBoxEffectObsolete().
+    bool hasBoxEffect() const
+    {
+        return hasBoxDecorationBackground() || style()->hasVisualOverflowingEffect();

[Xianzhu, 2015/03/18 22:44:19]

hasBoxDecorationBackground() correctly considers the background of document
element.

+    }
+
     // Obtains the nearest enclosing block (including this block) that contributes a first-line style to our inline
     // children.
     virtual LayoutBlock* firstLineBlock() const;
 
     // Called when an object that was floating or positioned becomes a normal flow object
     // again.  We have to make sure the render tree updates as needed to accommodate the new
     // normal flow object.
     void handleDynamicFloatPositionChange();
 
     // LayoutObject tree manipulation
@@ skipping 1379 matching lines @@
 void showTree(const blink::LayoutObject*);
 void showLineTree(const blink::LayoutObject*);
 void showLayoutTree(const blink::LayoutObject* object1);
 // We don't make object2 an optional parameter so that showLayoutTree
 // can be called from gdb easily.
 void showLayoutTree(const blink::LayoutObject* object1, const blink::LayoutObject* object2);
 
 #endif
 
 #endif // LayoutObject_h