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

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/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 610 matching lines @@
     // SVG renderers need to be invalidated when their children are laid out.
     // LayoutBlocks with line boxes are responsible to invalidate them so we can't ignore them.
     if (isSVG() || (isLayoutBlockFlow() && toLayoutBlockFlow(this)->firstLineBox()))
         return false;
 
     // In case scrollbars got repositioned (which will typically happen if the layout object got
     // resized), we cannot skip invalidation.
     if (hasNonCompositedScrollbars())
         return false;
 
+    // The document element always draws background even if it has no background specified.
+    // In non-slimming-paint mode, the invalidation rect of the LayoutView covers the area

[chrishtr, 2015/03/18 19:30:05]

I guess it's hard to do that invalidation on the document?

Maybe we should have a LayoutDocument subclass or something, to hande the
various isDocumentElement() calls sprinked throughout layout and paint.

[Xianzhu, 2015/03/18 19:36:28]

Will explore this way.

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

This seems not feasible because the layout object for document element may be of
different types, e.g. LayoutBlockFlow or SVGRoot or others depending on the
document type.

+    // needing paint invalidation.
+    if (RuntimeEnabledFeatures::slimmingPaintEnabled() && isDocumentElement())
+        return false;
+
     return rendererHasNoBoxEffect();
 }
 
 LayoutBlock* LayoutObject::firstLineBlock() const
 {
     return 0;
 }
 
 static inline bool objectIsRelayoutBoundary(const LayoutObject* object)
 {
@@ skipping 2577 matching lines @@
 {
     if (object1) {
         const blink::LayoutObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
     }
 }
 
 #endif