Paint solid color backgrounds which are equivalent to locally attached into scrolling contents layer

third_party/WebKit/Source/core/style/ComputedStyle.cpp

 /*
  * Copyright (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Adobe Systems Incorporated. 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 1250 matching lines @@
 {
     return allLayersAreFixed(backgroundLayers());
 }
 
 bool ComputedStyle::hasEntirelyLocalBackground() const
 {
     const FillLayer* layer = &backgroundLayers();
     for (; layer; layer = layer->next()) {
         if (layer->attachment() == LocalBackgroundAttachment)
             continue;
-        // Solid color layers with a background clip of the padding box can be treated
+        // Solid color layers with an effective background clip of the padding box can be treated
         // as local.
-        // TODO(flackr): We can handle other fill boxes with solid colors as long as they
-        // are essentially the same (i.e. PaddingFillBox == ContentFillBox when padding = 0).
-        if (!layer->image() && !layer->next() && layer->clip() == PaddingFillBox)
-            continue;
+        if (!layer->image() && !layer->next()) {
+            EFillBox clip = layer->clip();
+            if (clip == PaddingFillBox)
+                continue;
+            // A border box can be treated as a padding box if the border is opaque or there is
+            // no border.
+            if (clip == BorderFillBox
+                && (borderTopWidth() == 0 || !visitedDependentColor(CSSPropertyBorderTopColor).hasAlpha())
+                && (borderLeftWidth() == 0 || !visitedDependentColor(CSSPropertyBorderLeftColor).hasAlpha())
+                && (borderRightWidth() == 0 || !visitedDependentColor(CSSPropertyBorderRightColor).hasAlpha())
+                && (borderBottomWidth() == 0 || !visitedDependentColor(CSSPropertyBorderBottomColor).hasAlpha())) {
+                continue;
+            }
+            // A content fill box can be treated as a padding fill box if there is no padding.
+            if (clip == ContentFillBox
+                && paddingTop().isZero()
+                && paddingLeft().isZero()
+                && paddingRight().isZero()
+                && paddingBottom().isZero()) {
+                continue;
+            }
+        }
         return false;
     }
     return true;
 }
 
 const CounterDirectiveMap* ComputedStyle::counterDirectives() const
 {
     return m_rareNonInheritedData->m_counterDirectives.get();
 }
 
@@ skipping 752 matching lines @@
         if (value < 0)
             fvalue -= 0.5f;
         else
             fvalue += 0.5f;
     }
 
     return roundForImpreciseConversion<int>(fvalue / zoomFactor);
 }
 
 } // namespace blink