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

chrome/browser/system_monitor/removable_device_notifications_mac.mm

 // 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.
 
 #include "chrome/browser/system_monitor/removable_device_notifications_mac.h"
 
 #include "content/public/browser/browser_thread.h"
 
 namespace chrome {
 
@@ skipping 107 matching lines @@
       device_info->name = info.display_name();
       device_info->location = info.mount_point().value();
       return true;
     }
     current = current.DirName();
   }
 
   return false;
 }
 
+void RemovableDeviceNotificationsMac::StartWatchingStorage(
+    const FilePath& path) {
+  NOTIMPLEMENTED();
+}
+
+void RemovableDeviceNotificationsMac::StopWatchingStorage(
+    const FilePath& path) {
+  NOTIMPLEMENTED();
+}
+
 // static
 void RemovableDeviceNotificationsMac::DiskAppearedCallback(
     DADiskRef disk,
     void* context) {
   RemovableDeviceNotificationsMac* notifications =
       static_cast<RemovableDeviceNotificationsMac*>(context);
   GetDiskInfoAndUpdate(notifications->AsWeakPtr(),
                        disk,
                        UPDATE_DEVICE_ADDED);
 }
@@ skipping 40 matching lines @@
       it = disk_info_map_.begin(); it != disk_info_map_.end(); ++it) {
     if (it->second.mount_point() == mount_point) {
       *info = it->second;
       return true;
     }
   }
   return false;
 }
 
 }  // namespace chrome