Convert JsonWriter::Write to taking a const ref for the in-param

extensions/browser/api/cast_channel/cast_channel_api.cc

Index: extensions/browser/api/cast_channel/cast_channel_api.cc
diff --git a/extensions/browser/api/cast_channel/cast_channel_api.cc b/extensions/browser/api/cast_channel/cast_channel_api.cc
index e00646e5858f289f30bfe872a8e6a60b49ce973a..4ad8624b07648c0b7903c62393ca0d5c45f2a0c4 100644
--- a/extensions/browser/api/cast_channel/cast_channel_api.cc
+++ b/extensions/browser/api/cast_channel/cast_channel_api.cc
@@ -59,7 +59,7 @@ template <class T>
 std::string ParamToString(const T& info) {
   scoped_ptr<base::DictionaryValue> dict = info.ToValue();
   std::string out;
-  base::JSONWriter::Write(dict.get(), &out);
+  base::JSONWriter::Write(*dict, &out);
   return out;
 }