tracing: Make ConvertableToTraceFormat move-only scoped_ptr

cc/debug/rendering_stats_unittest.cc

Index: cc/debug/rendering_stats_unittest.cc
diff --git a/cc/debug/rendering_stats_unittest.cc b/cc/debug/rendering_stats_unittest.cc
index 6784e09f66b76f01fb284f9a940ad1ed30f09a0a..e8e0bff8c5c6a2640247ffab33c171ccd8abf3de 100644
--- a/cc/debug/rendering_stats_unittest.cc
+++ b/cc/debug/rendering_stats_unittest.cc
@@ -13,8 +13,7 @@ namespace cc {
 namespace {
 
 static std::string ToString(const RenderingStats::TimeDeltaList& list) {
-  scoped_refptr<base::trace_event::TracedValue> value =
-      new base::trace_event::TracedValue();
+  auto value = make_scoped_ptr(new base::trace_event::TracedValue);
   list.AddToTracedValue("list_value", value.get());
   return value->ToString();
 }