Set up clip and scroll parents on the blink side.

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index 96d3a7e4506632712e58b04af6d1e62fdd18eaf4..6801e4662ef9bb6cd009f21dfef130d74e575c9c 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -1812,6 +1812,19 @@ RenderLayer* RenderLayer::removeChild(RenderLayer* oldChild)
     return oldChild;
 }
 
+bool RenderLayer::hasAncestor(const RenderLayer* ancestor) const
+{
+    if (!ancestor)
+        return false;
+
+    for (const RenderLayer* layer = this; layer; layer = layer->parent()) {
+        if (layer == ancestor)
+            return true;
+    }
+
+    return false;
+}
+
 void RenderLayer::removeOnlyThisLayer()
 {
     if (!m_parent)
@@ -4895,10 +4908,11 @@ void RenderLayer::calculateClipRects(const ClipRectsContext& clipRectsContext, C
 
     ClipRectsType clipRectsType = clipRectsContext.clipRectsType;
     bool useCached = clipRectsType != TemporaryClipRects;
+    bool isRoot = this == clipRectsContext.rootLayer;
 
     // For transformed layers, the root layer was shifted to be us, so there is no need to
     // examine the parent.  We want to cache clip rects with us as the root.
-    RenderLayer* parentLayer = clipRectsContext.rootLayer != this ? parent() : 0;
+    RenderLayer* parentLayer = isRoot ? 0 : parent();
 
     // Ensure that our parent's clip has been calculated so that we can examine the values.
     if (parentLayer) {
@@ -4907,6 +4921,8 @@ void RenderLayer::calculateClipRects(const ClipRectsContext& clipRectsContext, C
         else {
             ClipRectsContext parentContext(clipRectsContext);
             parentContext.overlayScrollbarSizeRelevancy = IgnoreOverlayScrollbarSize; // FIXME: why?
+            if (this == clipRectsContext.scrollParent)
+                parentContext.scrollParent = 0;
             parentLayer->calculateClipRects(parentContext, clipRects);
         }
     } else
@@ -4923,8 +4939,21 @@ void RenderLayer::calculateClipRects(const ClipRectsContext& clipRectsContext, C
     else if (renderer()->style()->position() == AbsolutePosition)
         clipRects.setOverflowClipRect(clipRects.posClipRect());
 
-    // Update the clip rects that will be passed to child layers.
-    if ((renderer()->hasOverflowClip() && (clipRectsContext.respectOverflowClip == RespectOverflowClip || this != clipRectsContext.rootLayer)) || renderer()->hasClip()) {
+    // Update the clip rects that will be passed to child layers. There are two reasons
+    // we may ignor the cilp here. If we've been told to ignore the overflow clip (via
+    // ClipRectsContext::respectOverflowClip), we do so, but only if this is the clip
+    // root (this setting only applies to the root layer). Also, if a scroll parent is
+    // set, we ignore all clips until we've reached it (the point of the scrollParent
+    // member of ClipRectsContext is to determine the clip the scrollParent establishes
+    // with respect to the clipRoot, regardless of any subsequent clipping that may happen
+    // between us and our scroll parent).
+    bool shouldIgnoreClip = clipRectsContext.scrollParent && this != clipRectsContext.scrollParent;
+    bool shouldIgnoreOverflowClip = clipRectsContext.respectOverflowClip == IgnoreOverflowClip && isRoot;
+
+    bool shouldApplyClip = renderer()->hasClip() && !shouldIgnoreClip;
+    bool shouldApplyOverflowClip = renderer()->hasOverflowClip() && !shouldIgnoreOverflowClip && !shouldIgnoreClip;
+
+    if (shouldApplyOverflowClip || shouldApplyClip) {
         // This layer establishes a clip of some kind.
 
         // This offset cannot use convertToLayerCoords, because sometimes our rootLayer may be across
@@ -5438,6 +5467,29 @@ GraphicsLayer* RenderLayer::layerForScrolling() const
     return m_backing ? m_backing->scrollingContentsLayer() : 0;
 }
 
+GraphicsLayer* RenderLayer::layerForScrollChild() const
+{
+    // If we have an ancestor clipping layer because of our scroll parent, we do not want to
+    // scroll that clip layer -- we need it to stay put and we will slide within it. If, on
+    // the other hand, we have an ancestor clipping layer due to some other clipping layer, we
+    // want to scroll the root of the layer's associate graphics layer subtree. I.e., we want it
+    // and its clip to move in concert.
+
+    if (!backing())
+        return 0;
+
+    if (backing()->hasAncestorScrollClippingLayer()) {
+        return backing()->hasAncestorClippingLayer()
+            ? backing()->ancestorClippingLayer()
+            : backing()->graphicsLayer();
+    }
+
+    if (renderer()->containingBlock()->enclosingLayer() == ancestorScrollingLayer())
+        return backing()->graphicsLayer();
+
+    return backing()->childForSuperlayers();
+}
+
 GraphicsLayer* RenderLayer::layerForHorizontalScrollbar() const
 {
     return m_backing ? m_backing->layerForHorizontalScrollbar() : 0;