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diff --git a/chrome/browser/chromeos/drive/file_write_watcher.h b/chrome/browser/chromeos/drive/file_write_watcher.h
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+++ b/chrome/browser/chromeos/drive/file_write_watcher.h
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+// Copyright 2013 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_CHROMEOS_DRIVE_FILE_WRITE_WATCHER_H_
+#define CHROME_BROWSER_CHROMEOS_DRIVE_FILE_WRITE_WATCHER_H_
+
+#include "base/callback_forward.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "chrome/browser/chromeos/drive/file_system_util.h"
+
+namespace base {
+class FilePath;
+}  // namespace base
+
+namespace drive {
+
+namespace file_system {
+class OperationObserver;
+}  // namespace file_system
+
+namespace internal {
+
+typedef base::Callback<void(bool)> StartWatchCallback;
+
+// The class watches modification to Drive files in the cache directory.
+// This is used for returning a local writable snapshot of Drive files from the
+// Save-As file dialog, so that the callers of the dialog can save to Drive
+// without any special handling about Drive.
+class FileWriteWatcher {
+ public:
+  explicit FileWriteWatcher(file_system::OperationObserver* observer);
+  ~FileWriteWatcher();
+
+  // Starts watching the modification to |path|. When it successfully started
+  // watching, it runs |callback| by passing true as the argument. Or if it
+  // failed, the callback is run with false.
+  // When modification is detected, it is notified to the |observer| passed to
+  // the constructor by calling OnCacheFileUploadNeededByOperation(resource_id).
+  //
+  // Currently, the modification is watched in "one-shot" manner. That is, once
+  // a modification is notified, the watch is deactivated for freeing system
+  // resources. As a heuristic to capture the real end of write operations that
+  // might be done by several chunked writes, the notification is fired after
+  // 5 seconds has passed after the last write operation is detected.
+  //
+  // TODO(kinaba): investigate the possibility to continuously watch the whole
+  // cache directory.
+  void StartWatch(const base::FilePath& path,
+                  const std::string& resource_id,
+                  const StartWatchCallback& callback);
+
+  // For testing purpose, stops inserting delay between the write detection and
+  // notification to the observer.
+  void DisableDelayForTesting();
+
+ private:
+  // Invoked when a modification is observed.
+  void OnWriteEvent(const std::string& resource_id);
+
+  class FileWriteWatcherImpl;
+  scoped_ptr<FileWriteWatcherImpl, util::DestroyHelper> watcher_impl_;
+  file_system::OperationObserver* operation_observer_;
+
+  // Note: This should remain the last member so it'll be destroyed and
+  // invalidate its weak pointers before any other members are destroyed.
+  base::WeakPtrFactory<FileWriteWatcher> weak_ptr_factory_;
+  DISALLOW_COPY_AND_ASSIGN(FileWriteWatcher);
+};
+
+}  // namespace internal
+}  // namespace drive
+
+#endif  // CHROME_BROWSER_CHROMEOS_DRIVE_FILE_WRITE_WATCHER_H_