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

cc/trees/single_thread_proxy.cc

Index: cc/trees/single_thread_proxy.cc
diff --git a/cc/trees/single_thread_proxy.cc b/cc/trees/single_thread_proxy.cc
index b3712b67734cd339b6a4dc4081377b07cc9f116c..97b06bc4894f892b1c2ba80b5aadf3500052d9c9 100644
--- a/cc/trees/single_thread_proxy.cc
+++ b/cc/trees/single_thread_proxy.cc
@@ -26,7 +26,8 @@
     LayerTreeHostSingleThreadClient* client,
     scoped_refptr<base::SingleThreadTaskRunner> main_task_runner) {
   return make_scoped_ptr(
-      new SingleThreadProxy(layer_tree_host, client, main_task_runner));
+             new SingleThreadProxy(layer_tree_host, client, main_task_runner))
+      .PassAs<Proxy>();
 }
 
 SingleThreadProxy::SingleThreadProxy(
@@ -313,8 +314,8 @@
         blocking_main_thread_task_runner());
     layer_tree_host_->DeleteContentsTexturesOnImplThread(
         layer_tree_host_impl_->resource_provider());
-    scheduler_on_impl_thread_ = nullptr;
-    layer_tree_host_impl_ = nullptr;
+    scheduler_on_impl_thread_.reset();
+    layer_tree_host_impl_.reset();
   }
   layer_tree_host_ = NULL;
 }