Initial scroll-blocks-on compositor integration

Source/core/rendering/RenderBox.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, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 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
@@ skipping 86 matching lines @@
 
 RenderBox::RenderBox(ContainerNode* node)
     : RenderBoxModelObject(node)
     , m_intrinsicContentLogicalHeight(-1)
     , m_minPreferredLogicalWidth(-1)
     , m_maxPreferredLogicalWidth(-1)
 {
     setIsBox();
 }
 
+LayerType RenderBox::layerTypeRequired() const
+{
+    // hasAutoZIndex only returns true if the element is positioned or a flex-item since
+    // position:static elements that are not flex-items get their z-index coerced to auto.
+    if (isPositioned() || createsGroup() || hasClipPath() || hasTransformRelatedProperty()
+        || hasHiddenBackface() || hasReflection() || style()->specifiesColumns()
+        || !style()->hasAutoZIndex() || style()->shouldCompositeForCurrentAnimations())
+        return NormalLayer;
+
+    // Ensure that explicit use of scroll-blocks-on creates a RenderLayer (since we might need
+    // it to be composited).
+    if (style()->hasScrollBlocksOn()) {
+        if (isDocumentElement()) {
+            ASSERT(style()->scrollBlocksOn() == view()->style()->scrollBlocksOn());
+            return NoLayer;
+        }
+        return NormalLayer;
+    }
+    if (hasOverflowClip())
+        return OverflowClipLayer;
+
+    return NoLayer;
+}
+
 void RenderBox::willBeRemovedFromTree()
 {
     if (m_rareData && m_rareData->m_spannerPlaceholder) {
         m_rareData->m_spannerPlaceholder->spannerWillBeRemoved();
         m_rareData->m_spannerPlaceholder = 0;
     }
     RenderBoxModelObject::willBeRemovedFromTree();
 }
 
 void RenderBox::willBeDestroyed()
@@ skipping 4404 matching lines @@
     computedValues.m_margins.m_end = marginEnd();
 
     setLogicalTop(oldLogicalTop);
     setLogicalWidth(oldLogicalWidth);
     setLogicalLeft(oldLogicalLeft);
     setMarginLeft(oldMarginLeft);
     setMarginRight(oldMarginRight);
 }
 
 } // namespace blink