Move FilePathWatcher to base/files.

content/common/file_path_watcher/file_path_watcher.cc

-// 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.
-
-// Cross platform methods for FilePathWatcher. See the various platform
-// specific implementation files, too.
-
-#include "content/common/file_path_watcher/file_path_watcher.h"
-
-#include "base/logging.h"
-#include "base/message_loop.h"
-
-FilePathWatcher::~FilePathWatcher() {
-  impl_->Cancel();
-}
-
-bool FilePathWatcher::Watch(const FilePath& path, Delegate* delegate) {
-  DCHECK(path.IsAbsolute());
-  return impl_->Watch(path, delegate);
-}
-
-FilePathWatcher::PlatformDelegate::PlatformDelegate(): cancelled_(false) {
-}
-
-FilePathWatcher::PlatformDelegate::~PlatformDelegate() {
-  DCHECK(is_cancelled());
-}
-