Allow layers that need squashing to draw into the squashing layer in some cases.

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 18e6c98024aa4ffa81209a36960c7ae22485de67..e246fb6e4e6fd19d02a893ed6d17431d0255dc8d 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -1134,6 +1134,26 @@ RenderLayer* RenderLayer::enclosingCompositingLayer(IncludeSelfOrNot includeSelf
     return 0;
 }
 
+RenderLayer* RenderLayer::containingGroupedLayer() const
+{
+    ASSERT(isAllowedToQueryCompositingState());
+
+    for (const RenderLayer* curr = this; curr; curr = curr->parent()) {

[abarth-chromium, 2014/05/05 21:37:40]

Is this the right parent chain to walk?  I would have expected you to walk the
parents in the Stacking tree...

[chrishtr, 2014/05/05 21:58:51]

Right this is I think the issue with this CL.

+        switch (curr->compositingState()) {
+        case NotComposited:
+            continue;
+        case PaintsIntoGroupedBacking:
+                return const_cast<RenderLayer*>(curr);
+            break;
+        default:
+            return 0;
+            break;
+        }
+    }
+
+    return 0;
+}
+
 RenderLayer* RenderLayer::enclosingCompositingLayerForRepaint(IncludeSelfOrNot includeSelf) const
 {
     ASSERT(isAllowedToQueryCompositingState());