[Sync] Move model_type* from syncable/ to base/

[Sync] Move model_type* from syncable/ to base/

Also move enum_set* to base/.

This is the first step in moving ModelType et al. to the syncer
namespace (from syncer::syncable).

Move PurgeStalePayload() back to sync_session.cc.

Move ModelTypePayloadMapFromRoutingInfo() to model_safe_worker.* and rename it to ModelSafeRoutingInfoToPayloadMap().

BUG=128060
TEST=


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=145236

[akalin, 2012-07-03 00:13:33]

Most of the touched files have only their headers changed.

[rlarocque, 2012-07-03 00:26:44]

LGTM.

[commit-bot: I haz the power, 2012-07-03 00:30:10]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/akalin@chromium.org/10690071/1

[commit-bot: I haz the power, 2012-07-03 01:30:59]

Change committed as 145236