Revert of cc: Remove use of PassAs() and constructor-casting with scoped_ptr. (patchset #6 id:120001 of https://codereview.chromium.org/609663003/)

Reason for revert:
scoped_ptr nullptr support needs to be reverted

Original issue's description:
> cc: Remove use of PassAs() and constructor-casting with scoped_ptr.
>
> Say you have class A and subclass B.
>
> Previously it was required to PassAs() a scoped_ptr<B> into a
> scoped_ptr<A>. This is no longer needed, so just use Pass(). For newly
> created scoped_ptrs, you can just use make_scoped_ptr always now.
>
> And when you want to return or assign an empty scoped_ptr(), you can
> now use nullptr directly.
>
> Also adds PRESUBMIT checks for:
> - return scoped<T>(foo). This should be return make_scoped_ptr(foo).
> - bar = scoped<T>(foo). This should be return bar = make_scoped_ptr(foo).
> - return scoped<T>(). This should be return nullptr.
> - bar = scoped<T>(). This should be return bar = nullptr.
>
> This also replaces p.reset() with p = nullptr; But it does not add a
> PRESUBMIT check for that because there are things other than scoped_ptr
> with a reset() function.
>
> R=enne@chromium.org
>
> Committed: https://crrev.com/7bb3dbede19d87f0338797756ffd738adc6bca08
> Cr-Commit-Position: refs/heads/master@{#297096}

TBR=enne@chromium.org,jamesr@chromium.org,vmpstr@chromium.org,danakj@chromium.org
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/608503005

Cr-Commit-Position: refs/heads/master@{#297106}

1 files changed, 5 insertions, 2 deletions

diff --git a/cc/layers/layer_unittest.cc b/cc/layers/layer_unittest.cc
index 846951d..3950cf2 100644
--- a/cc/layers/layer_unittest.cc
+++ b/cc/layers/layer_unittest.cc
@@ -78,7 +78,7 @@ class LayerTest : public testing::Test {
     grand_child3_ = NULL;
 
     layer_tree_host_->SetRootLayer(NULL);
-    layer_tree_host_ = nullptr;
+    layer_tree_host_.reset();
   }
 
   void VerifyTestTreeInitialState() const {
@@ -1144,7 +1144,10 @@ static bool AddTestAnimation(Layer* layer) {
                                            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());
 }