Bug 848560 (part 1) - dmd::ClearReports() needs to check if DMD is running before doing anything to avoid crashing.  r=jlebar.

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extra : rebase_source : bdd7a6d1654dfbf562bc534311869248eb3c8a4a
Bug 848560 (part 2) - Prevent memory reporters from being registered while about:memory's tests are running.  r=jlebar.

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extra : rebase_source : 3187fef1c6910b637788499de47bef6718018c0a
Bug 848560 (part 3) - Add support to about:memory for writing memory report dumps and reading gzipped memory report dumps.  code=nnethercote,maierman.  r=jlebar.

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extra : rebase_source : b93b45d1f4c22a388eedff890c19dc1952c576de