[Sync] Move //sync to //components/sync.

sync/js/js_backend.h

-// 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 JsEventHandler;
-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 SYNC_EXPORT JsBackend {
- public:
-  // Starts emitting events to the given handler, if initialized.
-  virtual void SetJsEventHandler(
-      const WeakHandle<JsEventHandler>& event_handler) = 0;
-
- protected:
-  virtual ~JsBackend() {}
-};
-
-}  // namespace syncer
-
-#endif  // SYNC_JS_JS_BACKEND_H_