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

cc/blink/web_animation_curve_common.cc

Index: cc/blink/web_animation_curve_common.cc
diff --git a/cc/blink/web_animation_curve_common.cc b/cc/blink/web_animation_curve_common.cc
index 8230fab67eb1a6310ca8bec6642e927869522ad9..5abcf10f9a61659b0fbaf13b56679d8332d3e1b1 100644
--- a/cc/blink/web_animation_curve_common.cc
+++ b/cc/blink/web_animation_curve_common.cc
@@ -20,9 +20,9 @@
     case blink::WebCompositorAnimationCurve::TimingFunctionTypeEaseInOut:
       return cc::EaseInOutTimingFunction::Create();
     case blink::WebCompositorAnimationCurve::TimingFunctionTypeLinear:
-      return nullptr;
+      return scoped_ptr<cc::TimingFunction>();
   }
-  return nullptr;
+  return scoped_ptr<cc::TimingFunction>();
 }
 
 }  // namespace cc_blink