Implement systemInfo.storage.onChanged event

chrome/browser/extensions/storage_info_observer.h

Index: chrome/browser/extensions/storage_info_observer.h
diff --git a/chrome/browser/extensions/storage_info_observer.h b/chrome/browser/extensions/storage_info_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..b3e7ad7641ff3a3eeb2daf68e9441270294d0dd7
--- /dev/null
+++ b/chrome/browser/extensions/storage_info_observer.h
@@ -0,0 +1,25 @@
+// Copyright (c) 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 CHROME_BROWSER_EXTENSIONS_STORAGE_INFO_OBSERVER_H_
+#define CHROME_BROWSER_EXTENSIONS_STORAGE_INFO_OBSERVER_H_
+
+namespace extensions {
+
+// Observes the changes happening on the disk storage, e.g. free space changes.
+class StorageInfoObserver {
+ public:
+  virtual ~StorageInfoObserver() {}
+
+  // Called from FILE thread when the storage free space changes. The
+  // |threshold| paremeter indicates the change threshold from which the
+  // callback get called.
+  virtual void OnStorageFreeSpaceChanged(const std::string& id,
+                                         double old_value,
+                                         double new_value,
+                                         int threshold) = 0;
+};
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_STORAGE_INFO_OBSERVER_H_