Add UNKNOWN = 0 values to enums

Add UNKNOWN = 0 values to enums that were added to the google3 version
in http://cl/364769061.

Bug: 172934905
Bug: 182579315
Test: build / treehugger only
Change-Id: Id14086856e52549d03b2fcde6c18aacaa594c916
1 file changed
tree: e4361cf3863657b89e9e14ea71db0891024f548b
  1. stats/
  2. OWNERS