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

cc/layers/painted_scrollbar_layer.cc

Index: cc/layers/painted_scrollbar_layer.cc
diff --git a/cc/layers/painted_scrollbar_layer.cc b/cc/layers/painted_scrollbar_layer.cc
index 83c12e8650950cb7448415eac3724b5a4cf90e66..65fb78d373bba77174dd9c5087b73396e34629be 100644
--- a/cc/layers/painted_scrollbar_layer.cc
+++ b/cc/layers/painted_scrollbar_layer.cc
@@ -23,7 +23,7 @@
 scoped_ptr<LayerImpl> PaintedScrollbarLayer::CreateLayerImpl(
     LayerTreeImpl* tree_impl) {
   return PaintedScrollbarLayerImpl::Create(
-      tree_impl, id(), scrollbar_->Orientation());
+      tree_impl, id(), scrollbar_->Orientation()).PassAs<LayerImpl>();
 }
 
 scoped_refptr<PaintedScrollbarLayer> PaintedScrollbarLayer::Create(
@@ -156,8 +156,8 @@
   // When the LTH is set to null or has changed, then this layer should remove
   // all of its associated resources.
   if (!host || host != layer_tree_host()) {
-    track_resource_ = nullptr;
-    thumb_resource_ = nullptr;
+    track_resource_.reset();
+    thumb_resource_.reset();
   }
 
   ContentsScalingLayer::SetLayerTreeHost(host);
@@ -214,8 +214,9 @@
 
   if (track_rect_.IsEmpty() || scaled_track_rect.IsEmpty()) {
     if (track_resource_) {
-      track_resource_ = nullptr;
-      thumb_resource_ = nullptr;
+      track_resource_.reset();
+      if (thumb_resource_)
+        thumb_resource_.reset();
       SetNeedsPushProperties();
       updated = true;
     }
@@ -223,7 +224,7 @@
   }
 
   if (!has_thumb_ && thumb_resource_) {
-    thumb_resource_ = nullptr;
+    thumb_resource_.reset();
     SetNeedsPushProperties();
   }