Collect more COW size data in SnapshotMergeReport.

Bug: 180535575
Test: manual test
Change-Id: Ie35aad243ed57406a963e136ddf91fc67f20d6ca
diff --git a/aosp/cleanup_previous_update_action.cc b/aosp/cleanup_previous_update_action.cc
index 55c5a73..6eaa35b 100644
--- a/aosp/cleanup_previous_update_action.cc
+++ b/aosp/cleanup_previous_update_action.cc
@@ -395,9 +395,9 @@
     return;
   }
 
-  uint64_t cow_file_size;
-  if (snapshot_->InitiateMerge(&cow_file_size)) {
-    merge_stats_->set_cow_file_size(cow_file_size);
+  snapshot_->UpdateCowStats(merge_stats_);
+
+  if (snapshot_->InitiateMerge()) {
     WaitForMergeOrSchedule();
     return;
   }