Revert of cc: Remove use of PassAs() and constructor-casting with scoped_ptr.

cc/layers/ui_resource_layer.cc

Index: cc/layers/ui_resource_layer.cc
diff --git a/cc/layers/ui_resource_layer.cc b/cc/layers/ui_resource_layer.cc
index 498ba335bae49cf99004fd616cd13fe4f9c5deb6..59fbe8307b2097186e9dd97dfee238fcedcfb7cc 100644
--- a/cc/layers/ui_resource_layer.cc
+++ b/cc/layers/ui_resource_layer.cc
@@ -69,7 +69,7 @@
 
 scoped_ptr<LayerImpl> UIResourceLayer::CreateLayerImpl(
     LayerTreeImpl* tree_impl) {
-  return UIResourceLayerImpl::Create(tree_impl, id());
+  return UIResourceLayerImpl::Create(tree_impl, id()).PassAs<LayerImpl>();
 }
 
 void UIResourceLayer::SetUV(const gfx::PointF& top_left,
@@ -112,7 +112,7 @@
 }
 
 void UIResourceLayer::RecreateUIResourceHolder() {
-  ui_resource_holder_ = nullptr;
+  ui_resource_holder_.reset();
   if (layer_tree_host() && !bitmap_.empty()) {
     ui_resource_holder_ =
         ScopedUIResourceHolder::Create(layer_tree_host(), bitmap_);
@@ -131,10 +131,11 @@
   if (ui_resource_holder_ && ui_resource_holder_->id() == resource_id)
     return;
 
-  if (resource_id)
+  if (resource_id) {
     ui_resource_holder_ = SharedUIResourceHolder::Create(resource_id);
-  else
-    ui_resource_holder_ = nullptr;
+  } else {
+    ui_resource_holder_.reset();
+  }
 
   UpdateDrawsContent(HasDrawableContent());
   SetNeedsCommit();