Remove LayerTreeImpl::SetRootLayerFromLayerListForTesting.

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index a3820cadf48c430da188832506f1aaff16456963..a7df62e8c6dd858923a2c41737eb89697855f1d9 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -273,10 +273,6 @@ void LayerTreeImpl::SetRootLayerForTesting(std::unique_ptr<LayerImpl> layer) {
   layer_tree_host_impl_->OnCanDrawStateChangedForTree();
 }
 
-void LayerTreeImpl::SetRootLayerFromLayerListForTesting() {
-  root_layer_for_testing_ = layer_list_.empty() ? nullptr : layer_list_[0];
-}
-
 void LayerTreeImpl::OnCanDrawStateChangedForTree() {
   layer_tree_host_impl_->OnCanDrawStateChangedForTree();
 }