tree eb744a9aae0835c072a95085d2f1ad6c891bb6aa
parent 0ecc8367e610ae64ee96fd221080d9fab525aa87
author Shawn Pearce <spearce@spearce.org> 1499893310 -0700
committer Shawn Pearce <spearce@spearce.org> 1503007611 -0700

reftable: scan and lookup reftable files

ReftableReader provides sequential scanning support over all
references, a range of references within a subtree (such as
"refs/heads/"), and lookup of a single reference.  Reads can be
accelerated by an index block, if it was created by the writer.

The BlockSource interface provides an abstraction to read from the
reftable's backing storage, supporting a future commit to connect
to JGit DFS and the DfsBlockCache.

Change-Id: Ib0dc5fa937d0c735f2a9ff4439d55c457fea7aa8