Bug 961883 (part 0) - Some tiny HashTable comment tweaks. r=luke.

--HG--
extra : rebase_source : 749b61ec992335aa5e2be63340e88b04ff236967
Bug 961883 (part 1) - Measure and report the SourceDataCache. r=benjamin.

--HG--
extra : rebase_source : b599e19fb681e972b1f6e184c44f5a726a61009f
Bug 961883 (part 2) - Measure and report the StoreBuffer. r=terrence.

--HG--
extra : rebase_source : f298f0373b7fee99eee7a62060f882d628f97eb2
Bug 961883 (part 3) - Measure and report the Nursery. r=terrence.

--HG--
extra : rebase_source : 6f12d47ca8cedc96b0dd0477ca4f71de08e47181