cc: Enable composited border-radius scrolling.

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index d3100f3daa802322ca072e5be186709b65020bce..7ec2bf6ea25ddb7e036d94025f988be499f459ab 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -426,6 +426,7 @@ void Layer::SetMaskLayer(Layer* mask_layer) {
   if (inputs_.mask_layer.get()) {
     // The mask layer should not have any children.
     DCHECK(inputs_.mask_layer->children().empty());
+    DCHECK_EQ(bounds().ToString(), inputs_.mask_layer->bounds().ToString());
 
     inputs_.mask_layer->RemoveFromParent();
     DCHECK(!inputs_.mask_layer->parent());