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

cc/layers/layer_unittest.cc

Index: cc/layers/layer_unittest.cc
diff --git a/cc/layers/layer_unittest.cc b/cc/layers/layer_unittest.cc
index 846951d896762dd318dd3e3a4fb9f50c62b67bb0..3950cf2946b28e5714a3f645269febfd3ba2f0c2 100644
--- a/cc/layers/layer_unittest.cc
+++ b/cc/layers/layer_unittest.cc
@@ -78,7 +78,7 @@
     grand_child3_ = NULL;
 
     layer_tree_host_->SetRootLayer(NULL);
-    layer_tree_host_ = nullptr;
+    layer_tree_host_.reset();
   }
 
   void VerifyTestTreeInitialState() const {
@@ -1144,7 +1144,10 @@
                                            0.7f,
                                            scoped_ptr<TimingFunction>()));
   scoped_ptr<Animation> animation =
-      Animation::Create(curve.Pass(), 0, 0, Animation::Opacity);
+      Animation::Create(curve.PassAs<AnimationCurve>(),
+                        0,
+                        0,
+                        Animation::Opacity);
 
   return layer->AddAnimation(animation.Pass());
 }