Retire Downgrade.TakeSnapshot.MoveExistingSnapshot.*

Bug: 1149461
Change-Id: I15ab9cc3c2db147e2dd9222840a5fc8752dc50fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2562229
Commit-Queue: Yann Dago <ydago@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Greg Thompson <grt@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833108}

chrome/browser/downgrade/snapshot_manager.cc

@@ -160,10 +160,10 @@ void SnapshotManager::TakeSnapshot(const base::Version& version) {
     auto move_target_dir = user_data_dir_.Append(kSnapshotsDir)
                                .AddExtension(kDowngradeDeleteSuffix);
     base::CreateDirectory(move_target_dir);
-    MoveFolderForLaterDeletion(
-        snapshot_dir, move_target_dir.AppendASCII(version.GetString()),
-        "Downgrade.TakeSnapshot.MoveExistingSnapshot.Result",
-        "Downgrade.TakeSnapshot.MoveExistingSnapshot.FailureCount");
+    // This succeeds more than 80% of the time.
+    MoveFolderForLaterDeletion(snapshot_dir,
+                               move_target_dir.AppendASCII(version.GetString()),
+                               nullptr, nullptr);
   }
 
   size_t success_count = 0;

tools/metrics/histograms/histograms_xml/others/histograms.xml

@@ -4375,8 +4375,24 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Downgrade.TakeSnapshot.MoveExistingSnapshot.FailureCount"
+    units="count" expires_after="2020-12-31">
+  <obsolete>
+    Removed in M89.
+  </obsolete>
+  <owner>grt@chromium.org</owner>
+  <owner>ydago@chromium.org</owner>
+  <summary>
+    The number of items within an existing snapshot directory that could not be
+    moved aside before replacing it with a newer snapshot.
+  </summary>
+</histogram>
+
 <histogram name="Downgrade.TakeSnapshot.MoveExistingSnapshot.Result"
     enum="BooleanSuccess" expires_after="2020-12-31">
+  <obsolete>
+    Removed in M89.
+  </obsolete>
   <owner>grt@chromium.org</owner>
   <owner>ydago@chromium.org</owner>
   <summary>