Merge branch 'stable-2.15'

* stable-2.15:
  StarredChangesUtil: Handle unexpected format of reviewed/unreviewed labels
  Fix migration of mute stars
  Test that change is reindexed when change is starred/unstarred
  Suggest "is:private" in autocompete
  Trigger GitRefUpdatedEvent when star labels are updated
  Trigger GitReferenceUpdated event when account or change sequence is updated
  Fix bad rounding of relative dates like '1 year, 12 months ago'
  Fix test of RelativeDateFormatter
  Trigger GitReferenceUpdated event when external IDs are updated
  Increase the value of GERRIT_FDS parameter
  Add rel="external" to link to CLA
  Fix invalid operator invalidating web session
  Address test flakiness in gr-project-detail-list
  Update patchset selector styles

Change-Id: I4ec66d2d53c9fbe98878fa02585724db2eda216a

polygerrit-ui/app/elements/core/gr-search-bar/gr-search-bar.js

@@ -51,6 +51,7 @@
     'is:open',
     'is:owner',
     'is:pending',
+    'is:private',
     'is:reviewed',
     'is:reviewer',
     'is:starred',