Bug 1074961 - Part 14: Make the ChunkPool list doubly-linked; r=sfink

--HG--
extra : rebase_source : e2c420ad61a10939a8f8c68ddf5cb4822474fe74
Bug 1074961 - Part 15: Replace ChunkPool::Enum with ChunkPool::Iter; r=sfink

--HG--
extra : rebase_source : 2dd355cb6e7b1bc0e80284bf784eb70eeed517f7
Bug 1074961 - Part 16: Use a ChunkPool instead of manual list twiddling to manage available chunks; r=sfink

--HG--
extra : rebase_source : 2740670a8572cb1fd92709b5b6d3e33ff57d8185
Bug 1074961 - Part 17: Use a direct pointer for the Chunk list's prev link; r=sfink

--HG--
extra : rebase_source : 66f02fe5c11a639f65ce7ccca7a3d45c463b4ca1