Sync: Add a SyncTypePreferenceProvider interface.

chrome/browser/sync/profile_sync_service.h

Index: chrome/browser/sync/profile_sync_service.h
diff --git a/chrome/browser/sync/profile_sync_service.h b/chrome/browser/sync/profile_sync_service.h
index 6ff5bf51d9f0d2418e833cb676b4e909cdb0efdb..bf1aa7b13d5f2cf8fe8067c611161dc0044befb2 100644
--- a/chrome/browser/sync/profile_sync_service.h
+++ b/chrome/browser/sync/profile_sync_service.h
@@ -54,6 +54,7 @@
 class Profile;
 class ProfileOAuth2TokenService;
 class ProfileSyncComponentsFactory;
+class ProfileSyncServiceDataTypeProvider;
 class SupervisedUserSigninManagerWrapper;
 class SyncErrorController;
 
@@ -300,6 +301,10 @@ class ProfileSyncService : public ProfileSyncServiceBase,
   void AddTypeDebugInfoObserver(syncer::TypeDebugInfoObserver* observer);
   void RemoveTypeDebugInfoObserver(syncer::TypeDebugInfoObserver* observer);
 
+  void AddDataTypeProvider(ProfileSyncServiceDataTypeProvider* provider);
+  void RemoveDataTypeProvider(ProfileSyncServiceDataTypeProvider* provider);
+  bool HasDataTypeProvider(ProfileSyncServiceDataTypeProvider* provider) const;
+
   // Asynchronously fetches base::Value representations of all sync nodes and
   // returns them to the specified callback on this thread.
   //
@@ -919,6 +924,9 @@ class ProfileSyncService : public ProfileSyncServiceBase,
   // want to startup once more.
   virtual void ReconfigureDatatypeManager();
 
+  // Collects required sync data types from |data_type_providers_|.
+  syncer::ModelTypeSet GetRequiredDataTypes();

[Marc Treib, 2014/07/30 11:42:50]

Might have to make this public, so the UI can adapt accordingly (e.g. disable
checkboxes in the sync config overlay).

+
   // Called when the user changes the sync configuration, to update the UMA
   // stats.
   void UpdateSelectedTypesHistogram(
@@ -1023,6 +1031,8 @@ class ProfileSyncService : public ProfileSyncServiceBase,
   ObserverList<browser_sync::ProtocolEventObserver> protocol_event_observers_;
   ObserverList<syncer::TypeDebugInfoObserver> type_debug_info_observers_;
 
+  std::list<ProfileSyncServiceDataTypeProvider*> data_type_providers_;
+
   syncer::SyncJsController sync_js_controller_;
 
   // This allows us to gracefully handle an ABORTED return code from the