Extend the capability of SystemMonitor to support watching storage free space change

chrome/browser/system_monitor/removable_device_notifications_mac.h

Index: chrome/browser/system_monitor/removable_device_notifications_mac.h
diff --git a/chrome/browser/system_monitor/removable_device_notifications_mac.h b/chrome/browser/system_monitor/removable_device_notifications_mac.h
index 70a3e19162ae39f4eda2d63bf0c79ac0b0ee5f57..a5b7fb7ddc36caac03f941c99d3bf5aeccfcb514 100644
--- a/chrome/browser/system_monitor/removable_device_notifications_mac.h
+++ b/chrome/browser/system_monitor/removable_device_notifications_mac.h
@@ -18,7 +18,8 @@ namespace chrome {
 // This class posts notifications to base::SystemMonitor when a new disk
 // is attached, removed, or changed.
 class RemovableDeviceNotificationsMac :
-    public base::SupportsWeakPtr<RemovableDeviceNotificationsMac> {
+    public base::SupportsWeakPtr<RemovableDeviceNotificationsMac>,
+    public base::SystemMonitor::StorageFreeSpaceDelegate {
  public:
   enum UpdateType {
     UPDATE_DEVICE_ADDED,
@@ -35,6 +36,10 @@ class RemovableDeviceNotificationsMac :
       const FilePath& path,
       base::SystemMonitor::RemovableStorageInfo* device_info) const;
 
+  // Overriden from SystemMonitor::StorageFreeSpaceDelegate.
+  virtual void StartWatchingStorage(const FilePath& path) OVERRIDE;
+  virtual void StopWatchingStorage(const FilePath& path) OVERRIDE;
+
  private:
   static void DiskAppearedCallback(DADiskRef disk, void* context);
   static void DiskDisappearedCallback(DADiskRef disk, void* context);