LogDog: Update to archival V2.

appengine/cmd/logdog_coordinator/vmuser/index.yaml

 # Copyright 2015 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.
 
 indexes:
 # These "query endpoint" indexes support timestamp-based querying. These should
 # be kept in sync with the indexes in:
 # appengine/logdog/coordinator/endpoints/logs/query_test.go
 - kind: LogStream
   properties:
   - name: Prefix
   - name: Created
     direction: desc
 
 - kind: LogStream
   properties:
   - name: Name
   - name: Created
     direction: desc
 
+  # (This index also supports the expired log stream archival backend cron.)
 - kind: LogStream
   properties:
   - name: State
   - name: Created
     direction: desc
 
 - kind: LogStream
   properties:
   - name: Purged
   - name: Created
@@ skipping 40 matching lines @@
   - name: _Terminated
   - name: Created
     direction: desc
 
 - kind: LogStream
   properties:
   - name: _Archived
   - name: Created
     direction: desc
 
-  # This index supports the tumble installation.
+# This index supports the tumble installation.
 - kind: tumble.Mutation
   properties:
   - name: ExpandedShard
   - name: TargetRoot
 
 # AUTOGENERATED
 
 # This index.yaml is automatically updated whenever the dev_appserver
 # detects that a new type of query is run.  If you want to manage the
 # index.yaml file manually, remove the above marker line (the line
 # saying "# AUTOGENERATED").  If you want to manage some indexes
 # manually, move them above the marker line.  The index.yaml file is
 # automatically uploaded to the admin console when you next deploy
 # your application using appcfg.py.