[SystemInfo API] Rewrite storage info provider using storage monitor impl.

chrome/browser/extensions/api/system_info_storage/storage_free_space_observer.h

Index: chrome/browser/extensions/api/system_info_storage/storage_free_space_observer.h
diff --git a/chrome/browser/extensions/api/system_info_storage/storage_free_space_observer.h b/chrome/browser/extensions/api/system_info_storage/storage_free_space_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..1d1957f5b74547ad76eb51411c63731e7e79c7f9
--- /dev/null
+++ b/chrome/browser/extensions/api/system_info_storage/storage_free_space_observer.h
@@ -0,0 +1,28 @@
+// 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_EXTENSIONS_API_SYSTEM_INFO_STORAGE_STORAGE_FREE_SPACE_OBSERVER_H_
+#define CHROME_BROWSER_EXTENSIONS_API_SYSTEM_INFO_STORAGE_STORAGE_FREE_SPACE_OBSERVER_H_
+
+#include <string>
+
+namespace extensions {
+
+// Observes the storage free space changes.
+//
+// StorageInfoProvider class maintains a StorageFreeSpaceObserver list for
+// storage devices' free space change event.
+class StorageFreeSpaceObserver {
+ public:
+  // Called when the storage free space changes.
+  virtual void OnFreeSpaceChanged(const std::string& transient_id,
+                                  double old_value, /* in bytes */
+                                  double new_value  /* in bytes */) = 0;
+ protected:
+  virtual ~StorageFreeSpaceObserver() {}
+};
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_API_SYSTEM_INFO_STORAGE_STORAGE_FREE_SPACE_OBSERVER_H_
+