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

cc/blink/web_animation_curve_common.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/blink/web_animation_curve_common.h"
 
 #include "cc/animation/timing_function.h"
 
 namespace cc_blink {
 
 scoped_ptr<cc::TimingFunction> CreateTimingFunction(
     blink::WebCompositorAnimationCurve::TimingFunctionType type) {
   switch (type) {
     case blink::WebCompositorAnimationCurve::TimingFunctionTypeEase:
       return cc::EaseTimingFunction::Create();
     case blink::WebCompositorAnimationCurve::TimingFunctionTypeEaseIn:
       return cc::EaseInTimingFunction::Create();
     case blink::WebCompositorAnimationCurve::TimingFunctionTypeEaseOut:
       return cc::EaseOutTimingFunction::Create();
     case blink::WebCompositorAnimationCurve::TimingFunctionTypeEaseInOut:
       return cc::EaseInOutTimingFunction::Create();
     case blink::WebCompositorAnimationCurve::TimingFunctionTypeLinear:
-      return scoped_ptr<cc::TimingFunction>();
+      return nullptr;
   }
-  return scoped_ptr<cc::TimingFunction>();
+  return nullptr;
 }
 
 }  // namespace cc_blink