sync: Move all the js_* files into a js/ subdirectory.

chrome/browser/sync/js_event_handler.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_EVENT_HANDLER_H_
-#define CHROME_BROWSER_SYNC_JS_EVENT_HANDLER_H_
-#pragma once
-
-// See README.js for design comments.
-
-#include <string>
-
-namespace browser_sync {
-
-class JsEventDetails;
-
-// An interface for objects that handle Javascript events (e.g.,
-// WebUIs).
-class JsEventHandler {
- public:
-  virtual void HandleJsEvent(
-      const std::string& name, const JsEventDetails& details) = 0;
-
- protected:
-  virtual ~JsEventHandler() {}
-};
-
-}  // namespace browser_sync
-
-#endif  // CHROME_BROWSER_SYNC_JS_EVENT_HANDLER_H_