https://cs.chromium.org/chromium/src/components/sync/model/model_type_change_processor.h?l=54
OnMetadataLoaded does not really convey the purpose of the method, which is to indicate to the processor that the type is ready to start syncing. It especially does not convey that you have to call it before sync can begin.
This isn't really an observer/event scenario, it's the bridge's responsibility to give the proc the metadata, and it's a pivotal point in their initialization. The name should at least try to communicate this.
Comment 1 by bugdroid1@chromium.org
, Jan 19 2017