revlog: remove _chunkbase since it is no longer used This was introduced in 2011 for the lwcopy feature but never actually got used. A similar hook can easily be reintroduced if needed in the future.

revlog: move chunk cache preload from revision to _chunks In case we don't have a cached text already, add the base rev to the list passed to _chunks. In the cached case this also avoids unnecessarily preloading the chunk for the cached rev.

revlog._chunks: inline getchunk We do this in a somewhat hacky way, relying on the fact that our sole caller preloads the cache right before calling us. An upcoming patch will make this more sensible. For a 20 MB manifest with a delta chain of > 40k, perfmanifest goes from 0.49 seconds to 0.46.

revlog.revision: fix cache preload for inline revlogs Previously the length of data preloaded did not account for the interleaved io contents. This meant that we'd sometimes have cache misses in _chunks despite the preloading. Having a correctly filled out cache will become essential in an upcoming patch.