Fix under-invalidation about view background change caused by body style change

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 1731 matching lines @@
 {
     ASSERT(style);
 
     if (m_style == style) {
         // We need to run through adjustStyleDifference() for iframes, plugins, and canvas so
         // style sharing is disabled for them. That should ensure that we never hit this code path.
         ASSERT(!isLayoutIFrame() && !isEmbeddedObject() && !isCanvas());
         return;
     }
 
+    // These are used later to check invalidation of document element caused by
+    // body background change. FIXME: This may be related to crbug.com/475115.
+    LayoutObject* oldViewBackgroundLayoutObject = nullptr;
+    LayoutView* layoutView = view();
+    if (RuntimeEnabledFeatures::slimmingPaintEnabled() && layoutView && isBody())
+        oldViewBackgroundLayoutObject = layoutView->backgroundLayoutObject();
+
     StyleDifference diff;
     if (m_style)
         diff = m_style->visualInvalidationDiff(*style);
 
     diff = adjustStyleDifference(diff);
 
     styleWillChange(diff, *style);
 
     RefPtr<ComputedStyle> oldStyle = m_style.release();
     setStyleInternal(style);
 
     updateFillImages(oldStyle ? &oldStyle->backgroundLayers() : 0, m_style->backgroundLayers());
     updateFillImages(oldStyle ? &oldStyle->maskLayers() : 0, m_style->maskLayers());
 
     updateImage(oldStyle ? oldStyle->borderImage().image() : 0, m_style->borderImage().image());
     updateImage(oldStyle ? oldStyle->maskBoxImage().image() : 0, m_style->maskBoxImage().image());
 
     updateShapeImage(oldStyle ? oldStyle->shapeOutside() : 0, m_style->shapeOutside());
 
     bool doesNotNeedLayoutOrPaintInvalidation = !m_parent;
 
     styleDidChange(diff, oldStyle.get());
 
+    if (RuntimeEnabledFeatures::slimmingPaintEnabled() && layoutView && isBody() && layoutView->backgroundLayoutObject() == this) {

[chrishtr, 2015/04/30 01:23:57]

How about always invalidating the LayoutView and the LayoutObject for its
background layout object as a pair, regardless of the reason?

[Xianzhu, 2015/04/30 04:46:39]

We don't need to invalidate the LayoutView, but the documentElementLayoutObject
which may paint the viewport background using body's background style.

Do you mean:
  if (isBody() && shouldDoFullPaintInvalidation()) // caused by style change
     documentElementLayoutObject->setShouldDoFullPaintInvalidation()
?

I'm afraid this would cause unnecessary invalidation of the document element
when e.g.
- the body is animating a style other than background
- the document element has background and the body is animating its own
background

Hopefully the code added in this CL will be removed when we resolve
crbug.com/475115.

[chrishtr, 2015/04/30 17:48:36]

Yeah I mean just always invalidating both if one of them is invalidated. Will it
really be a performance problem?

+        // The rootObject paints view's background. We need to invalidate it when
+        // view's background changes because of change of body's style.
+        if (LayoutObject* rootObject = document().documentElement()->layoutObject()) {
+            if (oldViewBackgroundLayoutObject != this
+                || (!oldStyle && m_style->hasBackground())
+                || (oldStyle && oldStyle->visitedDependentColor(CSSPropertyBackgroundColor) != m_style->visitedDependentColor(CSSPropertyBackgroundColor))
+                || (oldStyle && oldStyle->backgroundLayers() != m_style->backgroundLayers()))
+                rootObject->setShouldDoFullPaintInvalidation();
+        }
+    }
+
     // FIXME: |this| might be destroyed here. This can currently happen for a LayoutTextFragment when
     // its first-letter block gets an update in LayoutTextFragment::styleDidChange. For LayoutTextFragment(s),
     // we will safely bail out with the doesNotNeedLayoutOrPaintInvalidation flag. We might want to broaden
     // this condition in the future as we move layoutObject changes out of layout and into style changes.
     if (doesNotNeedLayoutOrPaintInvalidation)
         return;
 
     // Now that the layer (if any) has been updated, we need to adjust the diff again,
     // check whether we should layout now, and decide if we need to invalidate paints.
     StyleDifference updatedDiff = adjustStyleDifference(diff);
@@ skipping 1525 matching lines @@
 {
     if (object1) {
         const blink::LayoutObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
     }
 }
 
 #endif