[Sync] Add plumbing of context from client to server

sync/test/engine/mock_update_handler.h

Index: sync/test/engine/mock_update_handler.h
diff --git a/sync/test/engine/mock_update_handler.h b/sync/test/engine/mock_update_handler.h
index 8d11f9620de19630d3ee3cb120e7fbde060712db..9a99afcc4b92a5c5cd34bc6531bc8966a19cbf60 100644
--- a/sync/test/engine/mock_update_handler.h
+++ b/sync/test/engine/mock_update_handler.h
@@ -20,10 +20,14 @@ class MockUpdateHandler : public UpdateHandler {
   // UpdateHandler implementation.
   virtual void GetDownloadProgress(
       sync_pb::DataTypeProgressMarker* progress_marker) const OVERRIDE;
+  virtual void GetDataTypeContext(
+      sync_pb::DataTypeContext* context) const OVERRIDE;
   virtual void ProcessGetUpdatesResponse(
       const sync_pb::DataTypeProgressMarker& progress_marker,
       const SyncEntityList& applicable_updates,
       sessions::StatusController* status) OVERRIDE;
+  virtual void ProcessDataTypeContextMutation(
+      const sync_pb::DataTypeContext& mutated_context) OVERRIDE;
   virtual void ApplyUpdates(sessions::StatusController* status) OVERRIDE;
   virtual void PassiveApplyUpdates(sessions::StatusController* status) OVERRIDE;