[Sync] Rework SharedValue<T> into Immutable<T>

chrome/browser/sync/js/js_arg_list.h

 // Copyright (c) 2011 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.
 
 #ifndef CHROME_BROWSER_SYNC_JS_JS_ARG_LIST_H_
 #define CHROME_BROWSER_SYNC_JS_JS_ARG_LIST_H_
 #pragma once
 
 // See README.js for design comments.
 
 #include <string>
 
-#include "base/memory/ref_counted.h"
 #include "base/values.h"
-#include "chrome/browser/sync/util/shared_value.h"
+#include "chrome/browser/sync/util/immutable.h"
 
 namespace browser_sync {
 
-// A thread-safe wrapper around an immutable ListValue.  Used for
-// passing around argument lists to different threads.
+// A thin wrapper around Immutable<ListValue>.  Used for passing
+// around argument lists to different threads.
 class JsArgList {
  public:
   // Uses an empty argument list.
   JsArgList();
 
   // Takes over the data in |args|, leaving |args| empty.
   explicit JsArgList(ListValue* args);
 
   ~JsArgList();
 
   const ListValue& Get() const;
 
   std::string ToString() const;
 
   // Copy constructor and assignment operator welcome.
 
  private:
-  typedef SharedValue<ListValue, HasSwapMemFnTraits<ListValue> >
-      SharedListValue;
-  scoped_refptr<const SharedListValue> args_;
+  typedef Immutable<ListValue, HasSwapMemFnByPtr<ListValue> >
+      ImmutableListValue;
+  ImmutableListValue args_;
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_JS_JS_ARG_LIST_H_