Fix visual rect for background box painting in composited scrollers.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 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 421 matching lines @@
             squashingLayer->setNeedsDisplayInRect(enclosingIntRect(paintInvalidationRect), invalidationReason, object);
         }
     } else if (object.compositedScrollsWithRespectTo(*this)) {
         layer()->compositedLayerMapping()->setScrollingContentsNeedDisplayInRect(r, invalidationReason, object);
     } else if (usesCompositedScrolling()) {
         if (layer()->compositedLayerMapping()->shouldPaintBackgroundOntoScrollingContentsLayer()) {
             // TODO(flackr): Get a correct rect in the context of the scrolling contents layer to update
             // rather than updating the entire rect.
             const LayoutRect& scrollingContentsRect = toLayoutBox(this)->layoutOverflowRect();
             layer()->compositedLayerMapping()->setScrollingContentsNeedDisplayInRect(scrollingContentsRect, invalidationReason, object);
+            layer()->setNeedsRepaint();

[chrishtr, 2016/08/22 17:34:54]

Why is this line needed?

[wkorman, 2016/08/22 17:42:27]

Copying my comment from https://codereview.chromium.org/2254893005/#msg15

We need this due to subsequent invalidateDisplayItemClient() DCHECK:

DCHECK(!paintingLayer() || paintingLayer()->needsRepaint());
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/layout/La...

I have concern this change may be introducing over-painting for this particular
scroll/background situation, but note http://crrev.com/2235873002 already
introduced line 440 which invalidates a rect sized to the entire scrolling
contents. But perhaps calling PaintLayer::setNeedsRepaint() ends up acting as an
overly large hammer and I'm unaware? I'll see if this produces diff in repaint
text expectations for other layout tests.

[chrishtr, 2016/08/22 17:46:33]

No it's ok I think. Thanks for the context.

+            invalidateDisplayItemClient(*layer()->compositedLayerMapping()->scrollingContentsLayer(), invalidationReason);
         }
         layer()->compositedLayerMapping()->setNonScrollingContentsNeedDisplayInRect(r, invalidationReason, object);
     } else {
         // Otherwise invalidate everything.
         layer()->compositedLayerMapping()->setContentsNeedDisplayInRect(r, invalidationReason, object);
     }
 }
 
 void LayoutBoxModelObject::addOutlineRectsForNormalChildren(Vector<LayoutRect>& rects, const LayoutPoint& additionalOffset, IncludeBlockVisualOverflowOrNot includeBlockOverflows) const
 {
@@ skipping 684 matching lines @@
     if (rootElementStyle->hasBackground())
         return false;
 
     if (node() != document().firstBodyElement())
         return false;
 
     return true;
 }
 
 } // namespace blink