Add a FileWatcher to base/.

base/file_watcher.h

Index: base/file_watcher.h
diff --git a/base/file_watcher.h b/base/file_watcher.h
new file mode 100644
index 0000000000000000000000000000000000000000..1147d42a29c3625087359e83eb2b2bcb6a88ef2f
--- /dev/null
+++ b/base/file_watcher.h
@@ -0,0 +1,65 @@
+// Copyright (c) 2010 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.
+
+// This module provides a way to monitor a file for changes.
+
+#ifndef BASE_FILE_WATCHER_H_
+#define BASE_FILE_WATCHER_H_
+
+#include "base/basictypes.h"
+#include "base/ref_counted.h"
+
+class FilePath;
+class MessageLoop;
+
+// This class lets you register interest in changes on a file. The delegate
+// will get called whenever the file is changed, including created or deleted.
+// WARNING: To be able to get create/delete notifications and to work cross
+// platform, we actually listen for changes to the directory containing
+// the file.
+// WARNING: On OSX and Windows, the OS API doesn't tell us which file in the
+// directory changed.  We work around this by watching the file time, but this
+// can result in some extra notifications if we get other notifications within
+// 2s of the file having changed.
+class FileWatcher {
+ public:
+  class Delegate {
+   public:
+    virtual ~Delegate() {}
+    virtual void OnFileChanged(const FilePath& path) = 0;
+  };
+
+  FileWatcher();
+  ~FileWatcher() {}
+
+  // Register interest in any changes on the file |path|.
+  // OnFileChanged will be called back for each change to the file.
+  // Any background operations will be ran on |backend_loop|, or inside Watch
+  // if |backend_loop| is NULL.  Note: The directory containing |path| must
+  // exist before you try to watch the file.
+  // Returns false on error.
+  bool Watch(const FilePath& path, Delegate* delegate,
+             MessageLoop* backend_loop) {
+    return impl_->Watch(path, delegate, backend_loop);
+  }
+
+  // Used internally to encapsulate different members on different platforms.
+  class PlatformDelegate : public base::RefCounted<PlatformDelegate> {
+   public:
+    virtual bool Watch(const FilePath& path, Delegate* delegate,
+                       MessageLoop* backend_loop) = 0;
+
+   protected:
+    friend class base::RefCounted<PlatformDelegate>;
+
+    virtual ~PlatformDelegate() {}
+  };
+
+ private:
+  scoped_refptr<PlatformDelegate> impl_;
+
+  DISALLOW_COPY_AND_ASSIGN(FileWatcher);
+};
+
+#endif  // BASE_FILE_WATCHER_H_