Backed out 4 changesets (bug 978027) for suspicion of causing B2G debug mochitest shutdown hangs.

Backed out changeset 24e3dcfeccf4 (bug 978027)
Backed out changeset c2f4decd1d2f (bug 978027)
Backed out changeset a8bdec0445f1 (bug 978027)
Backed out changeset 0912de2bb07f (bug 978027)