sync: add WIFI_CREDENTIALS protobuf, ModelType, and preference

sync/util/data_type_histogram.h

Index: sync/util/data_type_histogram.h
diff --git a/sync/util/data_type_histogram.h b/sync/util/data_type_histogram.h
index 980d3cc7498197c631d3f614a19b2de9c2bbb9fb..4d1c4cfa0287a3a1744840dbdfcb70ce0610f219 100644
--- a/sync/util/data_type_histogram.h
+++ b/sync/util/data_type_histogram.h
@@ -123,6 +123,9 @@
       case ::syncer::ARTICLES: \
         PER_DATA_TYPE_MACRO("Article"); \
         break; \
+      case ::syncer::WIFI_CREDENTIALS:             \
+        PER_DATA_TYPE_MACRO("WifiCredential"); \
+        break; \

[pavely, 2014/10/24 23:00:34]

I think this change needs to be acompanied by change in
tools/metrics/histograms/histograms.xml

You can add histograms similar to Sync.FreqSyncedNotifications,
Sync.SyncedNotificationsAssociationTime and
Sync.SyncedNotificationsStartFailure.

[mukesh agrawal, 2014/10/25 00:39:43]

Done.

Note that I changed the prefix from WifiCredential to WifiCredentials. I think
that's more consistent with the existing datatypes. Please let me know if that's
incorrect.

       case ::syncer::PROXY_TABS: \
         PER_DATA_TYPE_MACRO("Tabs"); \
         break; \