tree a4a0b50c48301c585d2b4335572aa984c586560c
parent 84c71ac93350e9d1e781efeaeab64e4277d585bc
author Shawn Pearce <spearce@spearce.org> 1500312249 -0700
committer Shawn Pearce <spearce@spearce.org> 1500322834 -0700

Derive DfsStreamKey from DfsPackDescription

By making this a deterministic function, DfsBlockCache can stop
retaining a map of every DfsPackDescription it has ever seen.  This
fixes a long standing memory leak in DfsBlockCache.

This refactoring also simplifies the idea of setting up more
lightweight objects around streams.

Change-Id: I051e7b96f5454c6b0a0e652d8f4a69c0bed7f6f4