Separating ONC<->Shill translation from the ONC signature.

Moves the mapping between Shill's and ONC's field names out of the ONC signature into separate tables.

Adds a base_signature pointer to ONC value signatures and uses that to define an derived signatures with additional state fields.

The advantage of such derived ONC signatures is that we can have specialized validation that don't influence each other:
  - ONC with readonly state from Shill
  - ONC from UI (like the JS extension API)
Both will be derived from standard ONC.

This commit adds the first of these two specializations: ONC with Shill's state information.

TBR=stevenjb@chromium.org (for test/data changes)
BUG=147614, 157696
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=186156

[Greg Spencer (Chromium), 2013-03-01 23:48:59]

LGTM.  I like this arrangement: it's easier to follow and more flexible.

[commit-bot: I haz the power, 2013-03-04 09:24:56]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/pneubeck@chromium.org/12390017/2017

[commit-bot: I haz the power, 2013-03-04 10:51:46]

Retried try job too often on win_rel for step(s) unit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

[commit-bot: I haz the power, 2013-03-05 09:49:23]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/pneubeck@chromium.org/12390017/12002

[commit-bot: I haz the power, 2013-03-05 11:52:49]

Change committed as 186156