sync: Introduce control data types

sync/internal_api/public/base/model_type.h

Index: sync/internal_api/public/base/model_type.h
diff --git a/sync/internal_api/public/base/model_type.h b/sync/internal_api/public/base/model_type.h
index 20c8ffa19d0a37d860e9170c706d7e58dca0bcba..808d14697182646a3f595b3784e0f625b9c8b2ec 100644
--- a/sync/internal_api/public/base/model_type.h
+++ b/sync/internal_api/public/base/model_type.h
@@ -124,6 +124,18 @@ SYNC_EXPORT ModelType GetModelTypeFromSpecifics(
 // value (sibling ordering) for this item.
 bool ShouldMaintainPosition(ModelType model_type);
 
+// If this returns true, this type belongs in GROUP_CONTROL.  The syncer has
+// special code to deal with its encryption, update application and conflict
+// resolution, so it should not receive any 'generic' processing for those
+// purposes.
+bool IsControlType(ModelType model_type);
+
+ModelTypeSet ControlTypes();
+
+// The types in this set are expected to be downloaded by the time backend
+// initialization has finished.

[tim (not reviewing), 2012/08/22 22:42:28]

The concept of "early download types" should go in SyncBackendHost, which is the
thing responsible for making the request to download them early, and knows about
the fact that that needs to happen before it reports "backend initialized". 
Note that it can't request a config until the SyncManager reports
OnInitializationComplete, and does this work before reporting
OnBackendInitialized to higher layers.

[rlarocque, 2012/08/23 20:11:23]

Done.

+ModelTypeSet EarlyDownloadTypes();
+
 // Determine a model type from the field number of its associated
 // EntitySpecifics field.
 ModelType GetModelTypeFromSpecificsFieldNumber(int field_number);