[sync] Componentize sync: Part 6: Add more SYNC_EXPORTs to files in src/sync/

sync/js/js_backend.h

-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Copyright 2012 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 SYNC_JS_JS_BACKEND_H_
 #define SYNC_JS_JS_BACKEND_H_
 
 // See README.js for design comments.
 
 #include <string>
 
+#include "sync/base/sync_export.h"
+
 namespace syncer {
 
 class JsArgList;
 class JsEventHandler;
 class JsReplyHandler;
 template <typename T> class WeakHandle;
 
 // Interface representing the backend of chrome://sync-internals.  A
 // JsBackend can handle messages and can emit events to a
 // JsEventHandler.
-class JsBackend {
+class SYNC_EXPORT_PRIVATE JsBackend {
  public:
   // Starts emitting events to the given handler, if initialized.
   virtual void SetJsEventHandler(
       const WeakHandle<JsEventHandler>& event_handler) = 0;
 
   // Processes the given message and replies via the given handler, if
   // initialized.
   virtual void ProcessJsMessage(
       const std::string& name, const JsArgList& args,
       const WeakHandle<JsReplyHandler>& reply_handler) = 0;
 
  protected:
   virtual ~JsBackend() {}
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_JS_JS_BACKEND_H_