Support additional list merge policies.  In addition to the already-supported append (no suffix), these new policies are now available: prepend ("+"), replace ("="), and set-if-not-present ("?").
Support additional list merge policies.  In addition to the already-supported
append (no suffix), these new policies are now available: prepend ("+"),
replace ("="), and set-if-not-present ("?").

old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google