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..b0695be79ba9df4663b5d964296cb2e820b25eb6 100644
--- a/cc/debug/rendering_stats_unittest.cc
+++ b/cc/debug/rendering_stats_unittest.cc
@@ -13,8 +13,8 @@ namespace cc {
 namespace {
 
 static std::string ToString(const RenderingStats::TimeDeltaList& list) {
-  scoped_refptr<base::trace_event::TracedValue> value =
-      new base::trace_event::TracedValue();
+  scoped_ptr<base::trace_event::TracedValue> value(
+      new base::trace_event::TracedValue());
   list.AddToTracedValue("list_value", value.get());
   return value->ToString();
 }