[MediaGalleries] Mock the app data dir on Windows/Mac

chrome/browser/storage_monitor/test_storage_monitor_win.cc

Index: chrome/browser/storage_monitor/test_storage_monitor_win.cc
diff --git a/chrome/browser/storage_monitor/test_storage_monitor_win.cc b/chrome/browser/storage_monitor/test_storage_monitor_win.cc
index dafb597a16db75072661cc77f24b5da478f2bd58..e78b5e6bcb33c979ff1a68972389702307a34892 100644
--- a/chrome/browser/storage_monitor/test_storage_monitor_win.cc
+++ b/chrome/browser/storage_monitor/test_storage_monitor_win.cc
@@ -32,5 +32,9 @@ TestStorageMonitorWin::volume_mount_watcher() {
   return volume_mount_watcher_.get();
 }
 
+StorageMonitor::Receiver* TestStorageMonitorWin::receiver() const {
+  return StorageMonitor::receiver();
+}
+
 }  // namespace test
 }  // namespace chrome